A 180 fw will weigh have around 1500 lbs of water, depending on decor. If you're going salt its about 1800 lbs of water, again depending on decor and fill level. But then you have the stand and equipment...a dry 180 is just shy of 350 lbs (if i remember right), and then the stand is probably another 100 lbs(?). So before any filters you're already around 2000 lbs.
Placement will depend on the construction of your house. If you have an I beam under the tank you'll be fine, if its just wood i get nervous. If you're going to put on concrete, you have nothing to worry about.