“HivePress Blocks” isn’t a standalone extension provided by HivePress. However, several of the existing extensions will add Gutenberg compatible blocks which you can use to help customise and design your website.
And, yes, you’re able to build your site locally and then launch it when you’re ready. However, I believe you should remove your HivePress license key from your local server and transfer it to your live site afterwards to ensure you’re able to receive the latest updates, etc.
FYI: There’s also a spring discount available at the moment. Enjoy 25% off everything with SPRING26 coupon until Tuesday, March 31.