We want to keep our pricing simple, so it's just 1 type of upgrade, at least for now.

The data management, storage (and others) are really what you are paying for. The other features are just bonuses to make SeriousMD be able to adapt to different users. 

If the core process of scheduling and keeping records are the only parts you need, then just use that. You are not required to use all the features inside the app.