[Buff]

For the small areas you can get an edger. I've only had time to prime so far and will finish up the room this weekend. However, we painted a wall last summer (and did like 3 coats of primer, lol) and we used an edger. It is like a little rectangular pad with a handle, the pad is replaceable.

I've heard that if you are painting two different colours that you should paint the lighter colour first. So I'd assume that you want to paint over the darkest colour first.

You can clean rollers with soap and water. I used dish soap. It isn't perfect but you can get two or three uses out of the roller. More if you're good/lucky.

I don't have an exact technique to avoid lap lines. I find as you get closer to your last coat that you don't see the lap lines so much. I've actually wondered at times if I missed a small strip (though that is going back to the priming 3 times and painting another 2 or 3 coats.). This time I only primed once and I wasn't worried about lap lines as I knew there was going to be a few coats of paint. To avoid drip lines I just go over with drip line with the roller.