Without knowing exactly what you mean by infrastructure, I'm just going to assume that you mean product infrastructure (e.g. hosting, servers, etc.).

Basically you don't want to over optimize your infrastructure until you have a known or anticipated growth rate.

So you want to spend your initial round of funding on marketing and customer acquisition. You'll also want to be careful about not committing to CAC (customer acquisition costs) or CLV (customer lifetime value) because that is what you are trying to figure out.

Happy to jump on a call and talk about when it makes sense to think about focusing on infrastructure.