To me creating a back end banking system using a load of software that's very new and still very much developing is a risky move. Once they're in production bank back ends tend to be around for a LONG time (in my experience in UK FS there were a load of old back-end systems that were maintained out of necessity as they were too expensive to re-write and the product they supported was still in use)
To me banking back-end systems should be boring from a tech perspective. Use well known components where the limitations and downsides are well known, and also if it were me I'd use components that I could get a support contract for. You don't want to be relying on open source support at 3am on a Sunday when you hit some bug or other and the FCA is breathing down your neck to get your transactions processed in a timely manner.