Along the lines of what 00Ranger and LouisianaJeeper were saying, make sure you get the right kind of undercoating if using undercoating One type is an asphalt based, and IS NOT what you want. It remains "tacky" even when "dry", reaks of tar for days, and is a brownish black color. It will also slowly wear and wash off. The kind to get for what you are doing is a rubberized undercoating. It dries to a durable flat black rubber coating. It is also good to help deaden noises from rocks inside fenderwells.
I've also used flat black spray paint for small touchups. Depending how comfortable you are in your painting abilities will dictate what you want to tape up. Taping will be purely a judgement call (wind conditions, clearance around wheels, experience, etc). I do small touchups without taping anything, but am very careful while spraying. I also keep a rag and 3M Wax and Adhesive remover handy to remove any wet overspray.
Dave