I do this on a regular basis with the team of PM's and User Researchers I manage.
Happy to help. Feel free to schedule a call with me.

I have built and helped build more than a couple service backends for mobile apps.

You are much better off with a PaaS offering like Amazon's AWS/EC2, Heroku or Microsoft's Azure.
These services allow you to keep your costs low while you still haven't achieved scale and make it really easy to scale up your backend when you do.

Do let me know if you have further questions and all the best with your business.

First off, you need to validate:
1. this is indeed a problem for users
2. how do most users currently discover financing options? Is there a point in that user flow where the user would search for financing options beyond those readily available to them?
(ex. buying a car at a dealership, I would receive an option from the dealership, I'd check with my existing bank(s) if they could beat that rate and go with the lower of those two).
3. you can provide better rates/better convenience.

If all of the above check out, you have a valid opportunity.

Viability would now depend on the ability of your solution to:
1. Make users aware of your offering
2. Plug into their existing workflows
3. Provide better rates, faster than the status quo

All the best and feel free to reach out if I can help any further.