Hmm don't worry ... perfection is something you never reach but something you should strive for....
to put it into other words ... just do it. Don't let future might be eventualities block your idea! There is no perfect architecture, you will learn as you go and hate your own code after a while.
Maybe you don't need to integrated pricing but you can wrap it around ? have you thought to give every customer her/his own database to get rid of the multi tenant issue? Why make things complex in the code if you can push it on the architecture?
just relax, set your goals, move on, evaluate, and do it again.
Armin Ronacher the guy who is writing part of sentry and wrote flask, jinja and others said in one of his talks -> "just use what you know, don't try to be perfect in advance." this is ofc paraphrased.