I'ma run and get the popcorn! 

Start there, because you need to be coding. 

> 5. Do i wast my time...?

No. 

Inside3d.com is a good starting point, they've got a load of tutorials in QuakeC, the language you'll need to use to code up your mods. They've also got messageboards where a lot of knowledgeable coders/modders hang out. There are a load of coders here too, but generally it's more mapping focused. 

Thank you for your reply. I'll try to look trough stuff in Inside3d.com

But if someone else have something to all please go ahead. 

*to add 

As others have said, is the place to look for coding help, they have tons of resources available to help people such as yourself.

If it turns out that coding new enemies etc is not your thing, perhaps the "Quoth" mod for quake will suit you as it comes with a ton of flexible options for adding new stuff to your maps without you having to learn the Quake coding language. 

QC looks interesting and simple enough. So I'll give it a try :)
I even came up with the idea how to implement EXP and LVL system :)

Inside3D.com is great help. 

Sorry, I know a lot of hard work went into it, by people who I respect, but, well..

----

Qc is advanced scripting, basically. You will need a determined animator though, since coding without an end result is pretty depressing.

The animator / modeler has to be determined because the Quake formats are like a brick wall. All game formats are, but in Quake you're looking at dawn of video games technology.

Good luck. 

I guess you can start by reskinning, and giving monsters different weapons, such as arming ogres with nailguns, or editing their default weapons a bit.

Or you can have a sword as a HUD weapon: take death knight's sword and attach it to player's fist originally holding the axe. Most monster weapons are detachable, except the regular Knight's "spike" (sword) protruding from his fist.

NOTE: I don't know [i]right now[/i] what model editor to suggest. Last time, I picked up a shareware version of QME (lite). For being a demo, it limited me to 20 frames (not enough for monsters but enough for simple guns). However, I was pretty much able to do stuff like weapon detaching and reattaching (it's just a matter of dragging some things out). Try looking at the "Quake Terminus" for various editing utilities. 

there is a full version of qme floating around. quaketastic and/or quaddicted should have it. 

As well. It's a full patch that you apply over the shareware version. It doesn't work on 64bit though, even though the shareware does. 

I'm not a qc expert but I suggest this
to have your new modified monster seen by Quake:

- extract soldier.mdl(example) from quake/id1 paks and load it in your model editor of choice(qme?)

-modify it as you want(colors,skins,vertices..)
and then save it in the format .mdl

-rename it as soldier.mdl and put it in Quake/yourmod/progs folder where yourmod is the folder you MUST create under Quake folder in order to have Quake engine "see" your new creation

-then launch Quake from a commandline with parameter "-game yourmod" (without quotes)
and you're done(hopefully)
"-game yourmod"