Do you have to start a tank with liverock? NO - though it is a good way to start, the live rock, live sand is always a good way to start a tank off to natural filtration.
You can even use cheap base rock to start a tank, after a few months it will have the bacteria on it.
It all kinda depends on what type of tank your trying to setup.
Fish only
Fish only with live rock
Reef
Which one?
If you remember the 70's then you remember Undergravel filters and crushed coral. Please don't use either for a saltwater tank. I did, learned my lesson and moved on to the rock and sand method.
Thomas