we've used redis for our scheduled jobs and does a pretty good job. we still do use mongoDB for our 'main' data. the reason for the redis option was because we liked the 'kue' - https://github.com/learnboost/kue
I'd also agree that dealing with taxes on Stripe is much more complex than it should be. It could be that there is no way to simulate time. It would be nice to see how Stripe reacts after one month subscriptions, or at least a few days, to get a real sense of how pro-rated prices are calculated in practice. I'd also like to see a better way to test webhooks in two cases: 1. when they are not successful and 2. be able to test webhooks with your application specific parameters.