I think perhaps 'interests' should be, initially, independent from the user(s) that expressed it. Maybe just indicate interests, and a count of many people have expressed them, then clicking on an interest could give you more about those users.
As I user, I would expect to register, and then either '+' the existing interests that I also have, or add new ones. The taxonomy of 'interests' is probably the hardest thing to get right.
You're re-inventing a lot of UI paradigms, like editing an interest by clicking into something which doesn't look like an input field, and then clicking away to save it. You won't need to explain as much how to use it if you stick to more typical CRUD patterns. I'm not a fan of showing each interest in a rounded rectangle, and I don't think it will scale very far...
To verify an account is owned by a given user, you could ask them to (temporarily) add a code into their 'about' field.
You might get more registrations if you didn't ask for an email address.