First.. I have searched a lot today, and there are some great threads. Thanks to everyone who has posted their experiences on this subject.

Now my question.. how far do I need to break down the AR for painting? I plan to use Krylon. I know that isn't the best route, but my gun isn't spectacular and I want to give it a shot. I don't have an air compressor or such, so I am limited in the things I can try.

While I've never done this myself, I've heard that you can take out the bolt carrier and stuff that area with absorbant rags of some sort, like paper towels.  Or, you can just leave the ejection port cover closed (dust cover).  Aside from that, you can pretty much just paint it as is.  Be sure, of course, not to get any in the barrel or other small areas that would be inopertune.

-Take your AR,  fully assembled.

-Close the ejection port door, insert a mag and pull the stock off the buffer tube/receiver extension.   (If it is a fixed stock then disregard)

-Hang the AR from a string so you can paint it easily.   Don't forget to paint your stock.

-Get some  generic brand non chlorinated brake cleaner at the auto parts store, find the cheapest one they have.  All you are trying to do is degrease the outside of your gun.  Spray it all of the outside of the gun until it is totally degreased, then let it dry off for bout 5-10 minutes.  
-Tape up your optic's lense.

-Spray a light base coat.  I think the lightest color is best as a base coat, you can tone it down later.  

-let it dry.  Then start  painting it.  darker colors on high surfaces, lighter colors in the lower, shadowed areas.  You don't need to get crazy, you just want to break up the pattern of an all black gun. try to avoid tiger stripes and all that.  Random is good for camo.  

-Spraying through the zippered white mesh laundry bags (little holes) gives an interesting pattern.  As does spraying over little dead pine branches found at the base of most small pine trees.  You can get a little creative just don't go overboard.

-Remember light coats are best.  

-When your finished painting, Let the gun fully cure.  

-Take the tape off you optic.  Use some acetone and Q-tips/rag to get the paint off your iron sights and magazine.  Put the stock back on the buffer tube.  

-Go shoot the gun.

You don't have to break it down at all.  Degrease it VERY well, and the cheapo wallyworld $1 cans will work fine for this.

Spray VERY light coats, and warm in between coats with a hairdryer if you want great results.