I don't think this is the right approach. The entire point of startups is that they are just
starting up. A startup a few weeks in can run on a Raspberry Pi, but in three years they could need half a rack, or a couple dozen racks. Buying expensive hardware is pretty pointless when you already know that it will most likely be inadequate in a few months.
Not to mention that you need quite a lot of money and engineering resources to get it all up and running. And it's never one half rack because you also need to have a secondary site for disaster recovery and backup...
Running your own hardware makes sense once your cloud bill starts hitting five figures and your hardware needs have become predictable. Until you reach that point, you can save yourself a lot of headaches by just using managed cloud resources.