Can I hide my store while I am still setting it up?

You have two options:

1. Demo mode: new stores start in Demo, where the storefront can be browsed end to end but no orders can be placed. Good while you build and test.
2. Maintenance Mode: go to Settings → Web Settings → Maintenance Mode, tick Enable maintenance mode, pick one of the five full-screen designs and save. Visitors then see a "back soon" page instead of the shop.

When you are ready, untick maintenance mode and click Go live in the top bar. The checklist that opens lets you go live once Payment, Tax and Shipping are set up.