Don't feel shy about asking as many questions as you need. I've spent time on each side of the fence, both as researcher and participant, and understand the importance to both parties of being as comfortable as possible before you start.
Not all of these will apply to every study of course - medical trials will require a lot more investigation than just a quick anonymous survey, for example.
(Oh and by the way, you could use these questions for research in any field, not just autism)