Over here, we only started to seriously thinking about what we're doing once we were handling in the order of 10K transactions per second.
Once you are at that level, you're probably going to need optimizations specific to your application and a generic database hoster might not be able to help you anyways.
I get that as a startup you don't have people for everything, but can you really afford to outsource the knowledge about the central piece of your application where all the value is stored at?