I didn't read every article so please forgive me if I'm repeating some aspects. This is heavily fragmented because I'm holding my baby in one arm so again bear with me.
First off the compressor...
As stated you don't need a high HP or large tank BUT you will NEVER hear your tools complain for air from a larger and beefier compressor that pumps out higher CFMs without hiccuping. Just remember that the compressors HP is more useful for filling the tank. Get a decent sized tank that you can afford (larger the better). Imagine that you're going to use this for more than painting. Most automotive work requires less CFM but anything painting, buffing, sanding will require much higher CFMs (just so the compressor can keep up). You'd hate to stop halfway during a spray to wait for the compressor to fill up.
I still prefer oil vs. non oiled.
There are your standard 110V and 220V outlets that you need to consider. If your garage doesn't have 220v outlet you will need to have someone put it in (I've heard people do it but honestly I've never liked electrical fixes) so that's extra money. When I asked I think it was going to cost me over $500+ (cheap if you ask me) to put two in my garage. With the extra plugs my circuit would need to be beefed up as well so I opted NOT getting the 220V compressors (but hey are SO nice) because if my wires can't handle the load they'll constantly keep tripping.
I'd run a moisture separator and oiler so your tools will last longer. The one I purchased has a water collector, oiler and separate line for painting (you don't want oil in your paint line). It's roughly another $100+ but well worth the investment. If you're painting you should also run a few catch filters at the end of the line unless you have a really nice separator.
Now the gun...
I'm in the process of purchasing a HVLP spray gun. Although I'd love to rock a SATA ($300~$500+ for one gun) my budget will probably send me towards a Devilbliss ($200 for gun and some accessories) setup. If you can borrow a decent spray gun do it because I can ONLY justify spending gobs of money on a spray gun, tips, cups, etc. because unless you're really going to be doing this often it's not worth the extra money. I'm starting out with a low/mid level gun and seeing if I like it.
ETC...
Those are the easy things. The rest of your money and time will be spent prepping and purchasing small things like paper, tape, paint, wipes, fans, plastic, car parts, panels, welder, etc. These things add up REAL fast...
If I were to price everything just to get started with a compressor it would easily cost over $1,500+ for the compressor and parts (hoses, hose reel, fittings, swivel fittings, couplings, some basic tools like impact gun, ratchet, grinder, buffer). Add at least $300 for a decent paint gun (tips, cups, paint) and goodness who knows how much for the other small stuff like tape, covers, paint, filler, sandpaper, etc (just make it a nice $500). Pray your car doesn't have rust because now I'm looking at a decent welder (add another $800+ to that).
I know people can argue about costs and what not but these are basics. It's like budgeting for children; no matter HOW much you save you never really can save enough for it. Just be reasonable and have a budget so you don't go into debt.
Sorry it's long, hope this helps...