I think there’s a difference between being professional and having an overwhelming contract. I have a very brief, casual agreement instead of a massive contract, yet it’s still very professional, and I’ve gotten good feedback about it. Read more about it here:

How to work with freelance clients: the best contracts are the ones you never have to enforce

I don’t believe there is such a thing as over-communication, as long as it’s useful productive communication. But the right kind of communication may not entail throwing everything at them at once. If you’re worried that’s what you’re doing, perhaps break it down into only the most essential information to start, and then unfold the rest as your client relationship deepens.