Building a sports card marketplace as a non-developer — would love feedback

I've been working on a project called MintGemTen, a marketplace focused on buying and selling sports trading cards.

The idea is to create a cleaner and lower-fee alternative to some of the larger platforms that collectors currently use.

I'm not a professional developer, but I wanted to see how far I could get building a prototype myself before bringing in more experienced help. Using AI tools and a lot of trial and error, I was able to get a basic version working.

Right now the prototype includes:

• user accounts
• card listings
• image uploads
• a marketplace browsing page
• a simple seller tier system

The backend is currently running on Supabase.

The main thing I'm trying to figure out now is whether the current architecture is something that can be refactored into a solid MVP, or if parts of it should be rebuilt before moving forward.

I'm starting to talk with a few developers about reviewing the project, but I'd also love feedback from other builders here.

A few things I'm curious about:

If you've built a marketplace before, what were the biggest early technical mistakes you made?

Do you think Supabase is a reasonable backend choice for an early marketplace MVP?

At what point did you bring in more experienced developers?

This project started mostly as an experiment to see if I could get the concept working, but it's turning into something I'd really like to push forward.

Would love to hear thoughts from anyone who's built marketplaces or early stage products.