If you're taking rock out of an established tank, keeping it in the same system's water, and then reusing it in the new system, IME you generally won't see any significant "cycle" as there's usually not much die-off. It's a good idea to look the rock over when you pull it out though. If you have a lot of sponge growth, they can die-off and cause some trouble (although personally I've never had a problem with that). IMO, having a good skimmer running during all of this increases your safety margin in the event that there is some die-off.
As for the size system you can start-up, IMO you can pretty much setup whatever you want - the bioload in the next system will be the same (intially) as the old and you have enough rock to get started (again, IME). If the new system is going to be a lot larger, and therefore mostly new saltwater, I would acclimate the fish/corals gradually to avoid unnecessary stress. Eventually you'll probably want to add more live rock if the new system is significantly bigger - as always, just make sure the rock is well cured before you add it to an established system with fish/corals/inverts already in it.
JMO & HTH