So, first thing: I know very much how you feel- began mapping again recently after seeing JK2 (Those ISD-Bridge-Screens convinced me ;) ).
To anwser your questions (as far as I know):
1. It really doesn't depend on the resolution- I'm mapping at 1024x768 and it works just fine.
The (actually four) windows can be adjusted in almost any way, so that everyone can find his fav. positions.
2. If you can press the mouse-wheel down you actually HAVE a three-button mouse, elsewise I would recommend getting one (not only for mapping but for gaming too). As far as I got you do not need the mouse3-button, but a wheel is quite handy for zooming in and out.
3. Well for me it's all about the 'feel'. If you play a map for say 3 hours with your friends and can't get enough of it then you made a good map. You cannot say: build three stairs, 4 powerups, 5 weapons- add water, mix it and taddaaa: you have a perfect map. I think you need a nice image of what your map should look like- or a theme that you'll use as basic (example: An Ewok-Village as deathmatch; everytime you slip you'll fall from the trees and crater). Only one thing I always try to remember: Every room needs two entrances- one from which your attacker is coming and one as your escaping route. Only on a few occasions (like being the respawn of a powerful- level dominating weapon [like the redeemer in UT]) can be a reason to only leave one entrance.
4. I don't think you must be programmer to build good levels. My best levels are from a time when I didn't know how to fix Windows, so I pretty much think it's more about the 'skill' of turning the images in your head into solid maps.
One link I really found quite useful at the beginning was:
http://planetquake.com/bubba/tutorial.html) <- was mentioned in this forum already
Bubba really explains the basics of mapping at the right pace- I learned Radient in one afternoon, so I think he did a pretty good job ;)
So far for the advice I can offer.
Now I have a question: Perhaps we have some more experienced mappers here who can help me out:
I made a mirror mesh and want it to rotate. Now every time I assign the func_rotating to it the mirror goes nuts. Now I remember an early map of Q3 where they've done that (so it worked then...). Does anyone know how to get the mirror fixed? You can't assign the func to the misc_portal_face, so how do I do it?