Typically needs to be magically-infused calcite chalk for that traditional feeling that your new demon friend will appreciate and respect you for. If you can’t infuse the chalk yourself, store bought is fine but you might end up with unexpected results based on the source.
Depends on the type of model it is, a lot of the time. Anime egirl/eboy-styled avatars tend to be some of the worst offenders (often kitbashers who don’t know any better), while furry avatars tend to be really well optimized most of the time.
If you aim for medium, that’s generally sufficient.