Yes, you can buy the reader from a store, or borrow a friend's if you want it immediately.  Once your account is set up, its good to go.

As far as the limits ... up here in the Great White North I can advise that there is no limit to credit card purchases that we've encountered, unless the limit is imposed by the buyer's credit card company.  Debit cards have *tap* limit of $100 per transaction - same as in a store.  No limit if using the chip reader and PIN. You can't use debit with the swipe reader.