Sounds all pretty good. Delighted that you're choosing such a model and hope to collaborate.

On the term exchange vs broker dealer: if Alice and Bob exchange digital cash for digital cash, this is indeed an exchange settled through blockchains as soon as the money moves outside the exchange. This definition depends on the soundness of the settling algorithm - for example see the malleability issue. Bitcoin does not have a full accounting system, and the semantics are not clear. If an exchange XYZ settles trades between members that is not a true settlement via blockchain, just an internal settlement. But we can imagine a model where XYZ opens up the books, so to speak. That's what I call a distributed or transparent exchange (as opposed to P2P, which does not work IMO). But digital cash for fiat goes through central banks and therefore in that case the fiat institutions clear the trades, and impose restrictions through AML and other rules. Doing that as P2P is certainly not going to work.