What features should a payment app include if it combines chat, P2P transfers, and payments like Venmo?

This is a very open-ended question. What markets will you be operating in to start with is an important element towards gaining traction. For a global payments app, interoperability is a huge issue. Being able to natively send money across to another person who may/may-not have your app, seems to be a big play that would be unfolding in the years to come. No one has cracked the interoperability in payments completely yet (as say they have done so with phone based text messaging).

Another important aspect is micro (or small value) payments, especially when they are cross-border. Very difficult to so small value payments even when we are talking within the same wallet app.