Local loyalty program website, what should I use?

I am in the planning process for a "shop local" loyalty program, and I am not sure about which path would be the most suitable for this project.

The website should be used frequently (+ once a week) by about 10K users and could reach up to 35K users (max).
About 100 merchants will join.
Merchants are not going to change their workflow: No special codes will be handed out, and they won't enter data into a website either. The information will be scanned by the customers and sent to a team of VA who will manually enter points for the program.

The loyalty rewards points will serve for sweepstakes and be convertible for rewards.

Since most merchant partners will provide dynamic content, the use of a CMS would mostly be required.

Which CMS/platforms (or alternative path) would you recommend for this project?

I don't see any ready-made solution for what I need, and unless there is some simple solution already there, I don't mind investing money on doing it from scratch if I can scale up the revenues and also maybe monetize it as a solution for other marketers.

Any opinion will be greatly appreciated. Thanks !