From experience in startups, most of those unit tests will be obsolete in a few months and slow you down. Choose carefully what critical functionality you want to unit test, and only unit test that. Integration testing at an API level is usually much more useful (especially for functionality on your API that you know won't change by leaps and bounds again), then you test end-to-end, so you'll know whether you're breaking it or not for the client / customer which is more important than knowing that that everything is mathematically perfect.