Start out small and see how much space your average product page takes up, you can get a rough estimate for the total need based on that. Same deal with bandwidth, except that depends on the amount of visitors your site gets, so make sure to use analytics and performance tracking to see when it’s time to upgrade the hosting plan.

In theory, yes. However, I have heard stories of people running intro trouble. If you want to be sure, purchase your domain through an external registrar. That way, you always have full control over it. You can find some options here: https://createawebsitenow.com/how-to-register-domain-name/.