1. TBH, I need full set so having only one set would make my game look bad with its mismatching sprites or graphics. So I choose these:
- Tilesets
- Character sprites
- Items/Objects
- Environments
2. 64x64 pixels and higher would be fine for me.
3. If possible, I'd like character sprites to be in parts so I could mix n match them. And for background environments, I prefer them to be tilable so I could control the length of my levels.