Hello,
We use Hetzner hosting for our demos. Many of our users use Bluehost, LightSpeed< Siteground. So, choose the one that suits your needs most of all. Theme requirements you can find here - https://xstore.helpscoutdocs.com/article/60-xstore-theme-requirements
The Ajax “add to cart” timeframe depends on server response time and DB optimization structure.
Regards