Let me think about this. This is a question of usage. My instinct says ...
I would NEVER say #3 "fine to you".
I might say #2 "fine by you" as to say: « in my opinion ».
I would say "fine with you" if it was with me personally. #1 seems to be a personal thing. #2 seems to be an opinion thing.
I could substitute #2 with "That be fine according to me." or "That be fine in my opinion."
I could substitute #1 by saying "That would be fine with me personally."
1. Would that be fine with you?
2. Would that be fine by you?
3. ___Would that be fine to you?___
As for the second choice, I would never say #3. I'm still deciding if I like #2.
1. Would you be fine with that?
2. **Would you be fine by that?**
3. ___Would you be fine to that?___
Usage is very ticklish, and full of nuance. I had a very British education, outside the UK. When I first visited England, I found myself able to adapt quickly to UK English. But when I went north to Scotland, I lost all my references: it was like going back in time 300 years. Preposition usage especially was completely different in Scotland. When you go to McDonald's there, you "take away" your burger ("take out" in Canada). "Take Away" in my dialect means I'm confiscating the burger! :)
I'm an English teacher, living in French Quebec, originally from Newfoundland, living in central Canada. My personal dialect is eclectic.