I can’t provide you with code but share some thoughts regarding payments/escrow and user interface. I did some project design.
We are discussing a “real world” selling tool, that does not rely only on crypto stuff. So when doing such things the ESCROW functionality of blockchains are not complete, because you need to take bank accounts into account. -> So we are discussing plans to drop this kind of functionality. Since the move from ICO to regualted STO, regualations require automaticly a specifice regulated rules. So this can be shiftet to classical software without a media break.
Second users that are not aware of cryptostuff may be addressed and like to have blockchain access. So a GSN solution seems much better, because it avoids MetaMask.
Third, MetaMask provides for “normal buyers” a maximum of a bad user interface and MetaMask breaks all User Interface Design. We are afraid of loosing people. So our plans is to make solutions withoud MetaMask in any case it is possible.
So that’s may be a reason why you don’t find a lot of “front-end” stuff.
So this are just my personal thoughts.