It's definitely a grey area right now. Operating advice among bitcoin lawyers/founders is that custodial definitely requires MTL/MSB stuff. Guidance prior to the Samourai charges was that non-custodial services were safe from that stuff. Now the Samourai case will likely decide that absent a law like this getting passed.

Have you checked out Zaprite? They are a little more focused on the freelancer and direct invoice use case, but have been adding more Stripe-like features/products.