If I purchase a power app subscription, test it out for a month, then if I find I only need some apps, can I then cancel the subscription and buy the apps I need? And then not have to uninstall and reinstall the apps?
Yes, you can fancel subscription and buy apps instead. Any subscription or purchase basically allows you to downlload and update the apps. Turning a sub off temporarily prevents you from updating until you reactivate Pro plan To buy the app.