There are so many options it's tough to provide specific advice. Also, I'm not sure what your level of experience with this stuff is, so forgive me if I'm saying things you already know.
Plumbing tips:
Step 1: Determine your desired turnover. Some guys on here claim the world will come to an end if you run anything under 10x per hour, yet my water parameters are always on point and I only turn my tank over 2x per hour. Granted, my bio-load is probably less than most on here.
Step 2: Determine head height (how high does the pump need to push the water? Elbows and other fittings will add some but head height is the most important).
Step 3: Determine which pump(s) you would like to use that push your desired GPH at your given head height. Choosing the right pump is important because buying an inefficient pump can cost you a lot of money in the long run. Pumps run 24/7, so if you are running an energy hog, you are going to feel it every month on your electric bill. Laguna and Reeflo are typically among the most efficient pumps you can buy.
Step 4: Determine what size plumbing you will need to handle that type of flow.**
** Oversizing your plumbing (especially drains/overflows) is ALWAYS better than undersizing. You can always restrict flow with a ball valve or with a reducer fitting, but you cannot easily increase your drains/overflows. If you decide you want more flow and you are stuck with 1" drains, it's going to be a real headache to install larger drains to accommodate more flow.
Check this calculator out:
http://reefcentral.com/index.php/dra...flow-size-calc
Enter your desired GPH and it will provide the minimum drain size required to achieve that GPH.
1" drain will typically handle ~600GPH
1.5" drain will typically handle ~1,300GPH
2" drain will typically handle ~2,400GPH
On your tank, I would go with two 2" drains. If the pump you decide on pushes more than 3,000GPH, I would use 2" plumbing for your returns. If you choose to run two smaller pumps that push less than 3,000GPH (some people like to do this for redundancy, in case one pump fails, the other will still be doing it's thing) you could use 1.5" plumbing. If you use smaller plumbing in either scenario, you will not be mazimizing the pumps potential, due to the increased friction/head pressure of trying to push water quickly through undersized pipe.
The location of your returns should be at the water's surface, or through the top of your tank. This is to prevent a backsiphon that could overflow your sump if the return sits too low in the tank.
In regards to the sump, a 180G is plenty big.
Stand:I would recommend making the stand at least 40" tall so that you have room to work in the sump (especially since your have a tall sump). My sump is 20" tall and my stand is 36" tall and there isn't too much room to work when I'm changing out filter socks. Having a tall stand means you will have to overcome more head pressure, but the extra room to work underneath the tank is worth it. Plus, IMO a huge tank on a tall stand makes the tank look even bigger and more awesome. If you can, I would go with a steel stand; it'll give you more room under the tank, since a wooden stand will be a lot bulkier and take up a lot more real estate down there. Either would be fine, but IMO, steel is better.
Heating (assuming you are keeping tropical fish):
If the room temps stay at or above 70F, you should be fine with 1 to 2 watts per gallon. If temps drop below 70F, you might need a bit more wattage. There are lots of variables when it comes to heating, so it's tough to give advice without knowing more details about your proposed setup. If the room is cold, covers and insulating non-viewing panels are definitely going to help keep heating costs down.
You can check out my setup for some ideas (see link in my signature below). I'm not saying my setup is perfect, but it works ok. One thing I don't like, is the 3 internal overflow boxes. I prefer external overflow boxes...I know Pacumom has them on her huge tank. The benefit of external overflow boxes is that they do not take up space inside your tank, but the downside is that the tank cannot sit flush up against the wall (if you're doing an in-wall build like Pacumom, this wouldn't matter).
I think the most important thing is to take whatever budget you might have for the tank, and triple it to determine what you will actually end up spending on it. Big tanks are expensive!
