Have you looked into Appengine Flex. Appengine flex is a PaaS like heroku, and will scale up any docker container. Its a great solution for your early days, and when you do need to move to a 1000+ node cluster its easy to switch from Appengine Flex to kubernetes. You also might get a lot of free startup credits https://cloud.google.com/developers/startups/
(Disclaimer, I work for Google).
[1] https://cloud.google.com/appengine/docs/flexible/