Just my opinion - I'd get the rock first - put it in some cheap containers cycling w/ a powerhead and heater (cooking would be ideal; cooking = cycling w/o light to establish a strong bacterial and not algae base for nutrient uptake) so that when you do get set-up the tank, everything will be ready to go. At least it will cut down on the time you have to wait for the cycle to complete once you get the tank up and going.
It's a good way to get cheap rock from other hobbiests (covered with nasty caulerpa, or aiptasia anemones) - cook it to eliminate the bad stuff - and then use it in your tank - better than cycled rock from the store. The only downfall is that *ideally* you will want 2 months to cook it - but any amount of pre-cycling that you can do w/ it will help out down the road.