on which to fall

Yes, that works, but most native speakers will say “snow is a forgiving surface to fall on.”

Grammatically, yes, this is fine. I expect people will argue about the fact, however.

Prescriptive answer: Yes, that's a perfect sentence. Descriptive answer: Sure, but it's awkward. No one talks like that in real life. Just say "to fall on." If you are doing something formal, like taking a test or writing a paper, use the prescriptive answer as a guideline. If you're just having a conversation, writing a blog post, or in an otherwise informal environment, use the descriptive answer.

Yes, but if you're going to word it formally like that, I'd use upon instead of on. Otherwise instead of "on/upon which to fall" you can just say "to fall on," which is a more common way to say it.