Ask HN: What's everyone's API billing stack?

I'm building a simple MVP API and want to put a credit card swipe in front of it to see if people will pay for it. I expect to need:

* Developer portal -- self-serve subscription management, API key management, usage tracking, plus documentation

* Billing enforcement -- rate limits, hard quotas, metered overages

Ideal solution covers both, but I'll stitch vendors together if needed. I'm seeing things like Kong, Moesif, and Tyk so far. What are people actually using? How painful is initial setup, and how much ongoing maintenance does it take to keep running? Are you happy with whatever you picked?