(All of this related to the postpaid plans only.

There may be some cap somewhere on the unlimited, but as far as I can tell, they mean proper unlimited. The only conditional is that it's unlimited on device only. Tethering gets cut off at 2.5GB. Each data plan also comes with a (very small) amount of data roaming.

Tethering rules, you get tethering if you have a data plan.

The new postpaid plans have no contract at all service side. The only conditional is that you will sign a contract if you buy a phone from them and choose the installment plan. Then the contract is only in place to indicate the phone will be paid off should service end.