Given that you're centrally keeping customer financial assets, you're looking at a banking license. At that point, the question is not whether you need a lawyer, but how many.
"Note that the issuer/bank would not itself offer currency exchange". Neither the Fed nor the ECB do, and quite a few smaller commercial banks also do not offer currency exchange. Doesn't matter, still banks.
How many of the banking laws apply would depend on the customers, and services offered to these customers. So far you've only excluded currency exchange, which means that pretty much every banking law might still apply.
You seem slightly hung up on the digital part. That's not how the law works. You'll need a banking license where you're operating your bank, not where its infrastructure is located.
And yes, not meeting the requirements for registering a bank (whether financially, regulatory, or legally) will stop your idea in its tracks. This is one of the cases where "talk to a lawyer" might not be the appropriate response, but "hire a legal team".