Just go to Seller Admin > Account Preferences and set the "Make all items unavailable for purchase until" date to some point in the future; this can be the exact date you expect your site will be ready to accept sales again, at which point your buttons would automatically become active again, or you can just set it for some date far in the future and then just delete that date setting when you're ready to go live.
One thing to bear in mind about moving cart buttons around, while you can generally copy/cut and paste Add to Cart buttons from one place to another, we recommend always copying your View Cart code directly from Seller Admin. The clickable View Cart button itself does not incorporate the second half of your View Cart code which manages the overlay-style cart display "inside" your page, so that latter half of the code would be left behind if you copy/cut and paste just the View Cart button itself from one page to another. Your View Cart code is unique to you but the same for all your products, so you only need one block of View Cart code on each page.
