I agree with splitting the heating wattage in half and useing two. With only one you will have one warm area in the tank and by the time you get to the other side it will be alot cooler. Also if one of the heaters should malfuntion at least there is something there until you get the situation fixed.
Find yourself an RO/DI unit. You will be useing alot of water for setting this tank up, water changes and topping off. This will save you alot of money and headaches in the long run. Not to mention you know the history of the unit. You know when the filters where changed because you did it. You can't know that at stores unless they tell you, and are they telling you the truth???
Mix your water before you put it into the tank, Don't ever add salt to your tank, it will be DEADLY. Get all your test kits and have them there ready to use. You will need to test your water often. and it is best to have them there incase something starts to happen at 730 Sunday night. Most LFS are closed on Mondays, you may not be able to wait two days to test your water to see what is going on. Another reason to have your RO/DI unit on hand. You never know when there may be a problem and sometimes you need to take care of it right then and there.
You didn't mention a skimmer. You should have a protien skimmer on your tank. Powerheads to circulate the water through out the tank, you don't want any dead spots, can cause problems. Get a good themometer, you need to keep the tank at level temps.
Your lighting will depend on what you want to keep. Fish only, soft corals or the LPS's and SPS's. Once you decide what it is you want in your tank, then we can help you figure out what lighting to put on your tank.
Mostly be patient. Take your time. This hobby can not and will not be rushed. When you try, you will end up with alot of problems. Also, it's a good idea to set up you QT (quarinteen tank) now too.So it will be ready to go, for when you start buying fish, Never put a brand new fish in your display tank. Alway quarrentine fish for 2 to 4 weeks before you put them in your main tank.