As @umbrel pointed out, we witnessed many projects following precisely the same path, ended up in oblivion.
If you want to succeed, there are two questions that should be answered before even starting the development of such an app:
1. Do you have the offline business part sorted out?
- existing fiat remittance network
- bank accounts
- business registration
- compliance, AML&KYC checks, regulatory requirements, etc.
If this is ready, then the technical part is quite trivial.
2. How to remove friction on the end-user side?
24/7 client support over the phone, fast deposits/withdrawals, and UX - don't forget about UX.
I always thought that typing long codes using a phone keyboard may be error-prone. How about creating a primitive Android/iOS app that will handle SMS communications? It could read and send messages, simplifying most tasks. Automatic message formatting using numbers from the phone contacts list, simple balance checks in one click, fancy UX. You can even implement transaction signing in the app that way. Installed once - and then can be used without internet.
In short, if you have all the prerequisites checked, then blockchain is optional in your case since the users don't control their secret keys. M-Pesa works without blockchains and works well. If not – Stellar won't help you, sadly it may even slow down the process due to the regulatory vacuum.
Really hope that you will be able to push this through, but there are chances that you are approaching the task from the wrong direction. I've been there myself, multiple times - with cool software and without reliable partners that could carry the burden of real-world business problems.