Ok let’s think Subscription, well you may or not know that most payment gateways now have subscription management built into the services.
Stripe & Braintree are some of the services that I have worked with & would recommend.
If you have a complex subscription model then you may need to move to a dedicated subscription management service like Chargify or ProfitWell that can be integrated into your payment gateway & accounting system.
If you are just starting out with an MVP your subscription model should be simple & easy to understand to all users.
Most SaaS have a vertical and horizontal subscription model, that start from the basic to the more advanced and elite corporate models increasing in price with each model on the functions and features & providing a monthly annually split.
It is also a great idea to provide FREE access to all the functions and features for around 7 to 14 days if it’s feasible for your business.