1- Specific tools: lots of them. Good quality hand tools are a must, since much of your work will be hand work. Screwdrivers, chisels, files, rasps, scrapers, hammers in sizes from small to monstrous, vise blocks for ARs, magnifying lamps, you name it. A good set of assembly/disassembly manuals will really come in handy.
2- Most common job- DC&O (disassemble, clean and oil). Trigger adjustments, sight replacement, recoil pads, action smooting, fixing the bonehead oopsies people always seem to do to their guns all come in pretty regular.
3- Most gunsmiths take whatever walks in the door.
4- All questions are relevant to the asker, but they may seem kind of banal after you have been doing it for a few years.
5- I wish I had known years earlier that I was not going to make any serious money fixing guns.