I use Django a fair bit, and have come to enjoy it.

It would absolutely be suitable for what you're describing.

If it was me, I'd probably think about using docker-compose, to create nginx, django & btcpayserver containers, all running inside the same virtual network.

nginx to proxy incoming requests to your django app, which in turn handles all of your internal logic, and can reach out via API to fetch invoices from the btcpayserver instance...

the best bit about this type of architecture is that anything else you need along the way, you can just add an additional container to your docker-compose configuration. be it a database, Tor, lightning node, whatever....