Frog Tape saves lives (and lines). Use it for just about any and all detail projects. Definitely worth the extra $$.
I also like to keep a rattle can of spray texture around for all those "oooops". It can be a lifesaver as well and does a good job of "hiding" my less than perfect fixes.
Avoid the "accent" wall color especially if it is a deep tone (reds are pretty bad to get it to lay down and look "right"), especially in a gloss. Our big red monster has about 3 coats of pink pepto bismol primer with about 7 coats of color on top. Looks pretty good but was a nightmare to get it to look like it does.
There is definitely a difference in paint qualities. If you are painting a lot, I wouldn't go with the high end stuff. Chances are you will repaint, or change the color again eventually. I do notice a difference in the Sherwin Williams paint in terms of coverage, how it lays down, and hide. Definitely better than most big box brands.
Oh, one final tip. Make sure you save your paint formulas somewhere (even if you take a picture of them and keep them on your phone). You won't believe how often paint companies change their formulas, colors, or the tints that are added at the store. Without a formula you are relegated to a huge guessing game (ask me how I know) of trial and lots of errors. The color you "like" today can be "out of style" next month With a formula, at least you have a puncher's chance.