Ask HN: Building a small business reselling subscriptions

If you were to create a small business today for re-selling subscriptions, which tools would you use for doing so? It can be COTS software, FOSS, customer developed or anywhere in between. How would you do it?

The basic functionalities that would need to be covered:

- Website: Static content and order flow.

- Order flow: Implementation of processes to activate, deactivate subscriptions etc. The processes likely be manual or semi-manual initially, but would gradually be automated to integrate to third party APIs.

- Subscriptions: For general handling of subscriptions and attributes related to the subscription.

- Billing: Handling credit card recurring payments and one-time payments.

The goal should be to keep costs, maintenance and manual intervention to a minimum. How would you go about building this?