Generally, there are a couple of concerns when moving a tank, that depend on a few questions..
Is the tank up and running now? Are you buying the current contents if so?
First let's think about the livestock..
Do you have enough containers (feed troughs, clean plastic barrels with tops or bungs, sealable buckets, etc) to move as much of the existing water as you can? Do you have enough EXTRA containers on hand to set up to do a 50% water change once you get everything home?
How long is the trip, and what's the weather in between there and home? Is the vehicle the livestock will be traveling in open like the back of a pickup truck, or closed like a van? If open, how do you plan on maintaining the temperature? an inverter and a bunch of heaters?
Do you have enough large bags (and containers to hold them upright) to bag up the fish into small groups that won't kill each other during the ride? How about corals? And live rock? You really want to keep that wet if you're setting the tank back up immediately.
Is there any live sand to be moved? If so, how deep is it? If it's a DSB, you probably want to either start fresh, or rinse the sand before reusing it.
On to logistics..
How is the tank plumbed? How much of the plumbing will have to be cut to get things apart, versus screwed apart at unions, etc etc. Do you have enough spare plumbing parts of the appropriate size(s) to stitch things back together at home if you end up cutting a lot?
How many friends do you have that you'd trust with a corner of a tank that you just paid a lot of money for? How much beer and pizza will it cost to get them to help you out? hehe..
Do you need to rent a trailer or even a moving truck for a day to get the thing moved? Will it fit in the house without removing anything? If not, can you remove a window or a sliding door panel?
When you get the tank in your house, where will it sit, and what's the structure under it? If it's pier and beam or joist construction, can you sit the tank next to an exterior wall to minimize sag? Or shore up the floor from the crawlspace or basement?
Is there enough electrical amperage to handle the new, larger tank where it'll sit?
Assuming you get the tank moved, set back up, get the plumbing stitched back together, and all the live rock back in, lighting set up, and everything running, how long will it take for things to settle down before you can put the fish back in? If the water got really cold during the trip, you'll need to heat it up in a hurry. Do you have a temporary trough or tank you could use to house the fish and corals in until the mess settles in the moved tank?
I've moved tanks a few times, those are just some of the things that I've ran into.