1) Do you use a stylus?
I most often use an Apple Pencil, and/or my fingers. Make sure to check if you iPad can be used with an Apple pencil, some of the older ones cannot.
A lot of the works on this site were created using just my fingers, as I'm a bit of a bubblehead and was always losing my stylus. I recently found a way to keep my Apple pencil attached:
2) Where did you get your case?
I love my rotating cases, as it means I can work vertically or horizontally. They tend to be reasonably sturdy and I can get the paint off of them from using them in the studio. Ebay is a wonderful resource for these rotating cases--be sure to get one that fits your model:
3) What iPad should I get?
This all depends on when, how and where you intend to use it. I recommend starting out with one of the 9.7" ones, as it's big enough to paint on (the zoom features get used quite a bit), but not so big that it becomes too difficult to have with you all the time.--the 12.9" can be like carrying a laptop around in terms of size and weight, and the minis can often be too small to paint on. If you've never had one, you'll soon find that you can carry around your books, newspapers, magazines, music, art courses, as well as all that work related stuff like emails and documents...