Just keep it simple, and if you take off scale vertically while you then work on a scalable solution. Since most businesses fail, premature optimisation just means you're wasting time that could have gone on adding more features or performing more tests.

It's a trap many of us fall into - I've done it myself. But next time I'll chuck money at the problem, using whatever services I can buy to get to market as fast as possible to test the idea. Only when it's proven will I go back and rebuild a better product. I'll either run a monolith or 1-2 services on VPSs, or something like Google cloud run or the AWS equivalent.

Scaling something no one wants is pointless.