However, Trenchbroom seems limited to box maps (maps with right corners, at least) with an initial glance and I want to use my architectural studies to the fullest.

Much to learn, young Padawan...much to learn... 

Much better. This is why that cheatsheet would come in handy! 

http://kristianduske.com/trenchbroom/docs/

All you need is pretty much there. It's fairly simple and straightforward, gives you all the shortcuts you need.
In terms of geometry creation, it's simple to use and understand but you can create complex stuff quite quickly. It's also very good for making organic geometry like rockwork and natural landscapes. 

Did you miss the documentation that TB comes with?

It's also available from here: http://kristianduske.com/trenchbroom/docs/ 

I normally don't check docs (especially "good" ones!) because they're generally full of overly technical info useless to a novice. Almost no consideration given to using them as a reference as you work.

Trenchbroom is a breath of fresh air all around!

I'm building a nice little start-room for my first map right now. Thanks for the help guys!

Couple remaining questions.

How complex can the lighting get? For example, if I wanted the lightmap to be casting shadows of bars or (using those pyramidal post lights from the ID base maps) just be a thin slot pouring out horizontally, could I do that? What about spotlights? How would I go about doing these?

Is there any way to visualize the lighting other than compiling the map and running it?

Thanks again by the way, guys! 

unfortunately, there isn't much in the way of visualizing lights. as a beginner, you will just have to compile and check until you start to get a feel for the numbers.

you can check this out for a little more explanation of the settings you can give to lights: http://shoresofnis.com/post.php?postID=2

i would recommend you have little test rooms where you copy and paste the bits of the map you want to test out lighting on. once you have a good result, copy and paste that light entity. not only is it easier, but you'll get a more consistent look.

this might help visualize spotlights a bit: http://shoresofnis.com/img/fakeshadows/torchShadows3.jpg

if you have a really hard time, you can use target->targetname from lights to info_nulls. that way you always know where the spot is pointing.

the guide touches on spot lights a bit. 

It can do more :)

http://www.quaketastic.com/files/screen_shots/rift0wip.PNG

But, I'd recommend not trying doing such freeform stuff just yet - you'll (probably) get frustrated quickly since there are a lot of things you need to know about how BSP and the compilers work before you start pushing the limits.

I've got some general hints, since I can't be bothered just now referencing stuff (and what everyone's provided above is more than enough for you to get started with).

1. Set yourself deadlines - the hardest part of mapping is finishing
2. It doesn't have to be perfect; concentrate on what you know is weak, not everything
3. Learn to be critical, identify where and why something is wrong
4. You don't have to release your first map
5. Personally, I don't follow any of these, and you'll develop your own method as you learn :D

One I do follow though:

6. The journey is more important than the destination

Good luck! 

And especially thanks to ijed: his Warpspasm pack (played for the third time...) inspired me to try this again. Having him post a response to me is kind of like one of those teenage fangirl squee moments, except less squee and more arterial blood spurts, and less teenage fangirl and more hideous unhinged star-abortion. 

Nice screenshot! It looks so ... surprisingly un-Quake-like and pretty. Makes me want to go and take a walk there (I mean a real walk; not a run through a map shooting monsters). 

Ok, I'm getting a bit more intricate with my work. Clipping brushes was initially really hard to wrap my head around until a friend described it as cutting decorative pastries, and then it was suddenly perfectly easy to understand.

And now lighting is getting past the point of simple functionality, so I'm wanting to know about best practices.

1: Target engine/engine parameters? Is it "okay" of me to target Darkplaces with RT World Shadow enabled? I can't keep the spotlights from lighting stuff they shouldn't be otherwise, it seems. If such a tight requirement would be frowned upon, is there a light util that does semi-proper shadowing?

2: Colored lights require .lit files. I futzed with the engine a bit, and if .lits aren't loaded, those lights don't work at all! That's a catastrophe. Is it okay to require .lit capability in whatever engine the user decides to run it in for full playability? If not, is there a way to quickly and easily strip all the _color keys from a .map so I can just compile a .lit-ful and a .lit-less set?

I want the maximum number of people to be able to "enjoy" my maps, but I also don't want to have to compromise atmosphere, especially in a game that is so very atmospheric. I'm trying to figure out what the line is there. 

1) Making a first-time map for Darkplaces only is a guarantee that almost no-one will play it. What are you trying to do exactly with the spotlights? If you describe the problem then I'm sure we can help.

2) What exactly do you mean by "I futzed with the engine a bit"? I'm not sure what you are trying to do there - if the engine supports lit, the lights will be coloured, if not, they will be uncoloured, but should all appear correctly otherwise. 

If .lits aren't loaded you get greyscale lighting. Anything else is a bug. 

Darkplaces is broken, then. Blah. Disabling RT World turns off all colored lights entirely. I figured this was equivalent to disabling .lit support, given otherwise it changed very little other than general shading. My bad. Guess I'll be moving to another engine... Any suggestions? (I only liked DarkPlaces for the shadowing.)

I'm trying to get overlapping areas of light and shadow on the side of a room. I have a set of very narrow angle spotlights currently, because of attempts to use progressively narrower angles to fix the spotlights lighting all of the walls and the floor with no darker spots at all. No dice. 

If you want to try another engine, QuakeSpasm is a good choice. Crossplatform, some good usability and performance improvements, relatively GLQuake-faithful but also with rendering bugfixes. Lots of mappers and map-players use it. 

Quakespasm seems to be the de facto standard around here (so if your map works properly in just one engine, Quakespasm is probably the best choice, as you'll have the largest potential audience).

I have no knowledge of the technical side of things, though. Maybe there's simply a setting in DarkPlaces that needs to fiddled with. 

OK, here's my unsolicited 2 cents ...

You're going to have to let go. :) Quake is over 20 years old so you're not going to realize any great lighting schemes or whatever you have planned. Quake can look great, don't get me wrong. But on the whole, you have to go for broad strokes rather than specific lighting set ups. 

but Quake is only 19. 

I saw screenshots of a map with excellent light/shadow interplay using spotlights in parallel with overlapping edges. It was some kind of lava-castle type thing... don't remember name off the top of my head. But I just want to do something like what that map did! I'm not expecting some kind of rendering voodoo that instantly makes it work like a modern engine, just having working spotlights would be peachy. (Currently my best guess is the light util is treating them as regular lights...) 

I'll check out Quakespasm... The GLQuake faithfulness does make me a little uneasy, but that's only because I'm sorta uncomfortable with older OGL games in general. Bad memories of antediluvian gaming machines having random BSOD seizures. I'm sure I'll get over it. 

If .lits aren't loaded you get greyscale lighting. Anything else is a bug.

Little warning here: if you have an OUT OF DATE .lit file, it might be overriding the light settings in subsequent compilations. This might result in unconnected patterns of lighting, unexpected colours, or just the map failing to update in-engine as you recompile with new settings. 

The map jams might be helpful:
https://www.quaddicted.com/reviews/?filtered=mapjam
most/all maps have sources included, so if you see a lighting effect you like, you can check out how it was done.

Or, post a screenshot + map file. Spotlights can be a pain to set up, I haven't used them much but did use them a bit in jam3_ericw.
IIRC there are two choices, either set "mangle" "yaw pitch roll", or target the light to an info_null (?) which is the spotlight target. 

but which light compiler are you using? 

The .lits are up to date, I doublecheck timestamps before I copy over files to the id1/maps folder, to prevent unexpected frustration. Maybe it's just that colored spotlights don't work (i.e., you can have color or spotlights but not both)? That would be awful but manageable.

I'm using the latest version of light.exe available here: http://disenchant.net/utils/ as per FifthElephant's tutorial. I don't know any of the settings, however. Do I need to add something to the commandline to make it work well with certain lighting?

I'll see about grabbing a screenshot but this may take me some time (I'm technically at work...). 

The top map (The Living End?) is the one that has the spotlights, clearly visible, that I am trying to emulate. https://www.quaddicted.com/reviews/ne_lend_doom.html

I'd offer a screenshot, but I just tried the map in Quakespasm and there are no spotlights. None, not even the ugly kind. So at this point I'll link my awful piece of crap thing (technically I'm building the end room of my first map, and the proportions are actually wrong) and see if anyone can spot the problem... because I can't. Please excuse the hideousness, this is very far from final-touch-up. The missing wall is because I have yet to build the rest of the map, of course.

http://dropcanvas.com/khdtx/1 

Mangle looks strange. Try 0 -90 0 and an angle of 80 - 120 for a lightcone facing down.

Mangle is 0-360 around z-axis, 90(up) to -90(down), and 0.