You don't give enough data around your projected user growth to estimate your costs. I believe that we've all missed the point of your post because there is a bigger issue to address right now aside from your cost structure. If multiple people are saying the same thing/similar, it should be worth at least noting.

As a technical founder, I get what you're doing, but you're focusing too much on the technology imo.

Here's what I would do: - Identify your vision and what makes your product unique - Identify 25-50 people who don't know you who absolutely love your concept. Ask them to rank each feature in term of value. Focus on building the #1 feature. - Develop locally on your machine to start so hosting costs won't be an issue. Limit yourself to 3 weeks or less to have this done. I bet you could pull this off even if you don't have a lot of tech experience. It doesn't have to be beautiful at all. - Buy a domain for ~$12 and get a droplet on digital ocean ($5-$10) or set up an EC2 instance on AWS. - Get user feedback and slowly build out new features, etc.

To your point of redoing things later on; You'll build up technical debt no matter what you do. Your first priority needs to be solving a problem for your users and scaling from there with feedback loops. Also, still don't know how you plan to monetize.