For Vercel, the Hobby plan is quite generous (I had a lot of projects deployed on it before I upgraded), and is fine for personal and non-commercial projects. You can monitor the usage in the Vercel dashboard too to give you insight on what’s being used. Here’s some more detailed info on pricing.
For your backend on Supabase:
- you can also start off on the Supabase free tier with up to 2 projects (here are the pricing details)
- the custom domain is an optional add-on and you may not need one - here’s some more information about Custom Domains on Supabase. (The Supabase custom domain is different to the custom domain you’d set up on Vercel for your frontend, which your users would see, for your website. The one on Supabase is a custom domain for your API)
So in summary, you can have a sufficient start on both free tiers for both your frontend and backend - the pricing details I’ve linked should help give you an idea of what you can expect for each. 