I would think it's obvious that if you already have RSI, you're doing something wrong. The answer might not be a question of how many hours you practice, though, but of how you spend that time. I believe Leon Fleischer, who finally regained the use of his right hand after many years, has advised students not to do finger exercises, but only to work on their pieces. I think he had other tips as well. However I couldn't find any reference to that on the web.
In any event you should make taking better care of your hands your top priority, even if it means dropping out of music school for a while. This is not something to mess around with.
As for having more than one teacher at a time, I can't see how that would help anything. They're sure to have different ideas, want you to work on different pieces, etc. And wouldn't they inevitably find out about each other? I think it's kind of a bizarre idea...