You are in New Jersey so it might be worth check this link out to see if there are any incentives for DHW.
http://www.dsireusa.org/incentives/index.cfm?re=1&ee=1&spv=0&st=0&srp=1&state=NJ. Otherwise its a 30% tax credit for the installed cost. As long as its a SRCC rated system, the fed doesnt require a licensed installer but you local building code may.
Here is a package price for DIY systems that are SRCC rated. A rough rule of thumb is one panel per person. Builditsolar.com has home made designs but they wont qualify for the fed rebate.
http://www.altestore.com/store/Kits...4-People/Closed-Loop-AC-Powered-w-Tank/c1124/
Typical payback is usually 5 to 7 years.
I have a wood boiler that uses my oil controls and pumps to heat the house. One zone is to a hot water maker tank, which is bascially an insulated tank with a coil in it. During the winter, I use the SHW as a preheater upstream of the hot water maker, in the later spring through fall, I run the SHW direct as my hot water and bypass the hot water maker. The SHW tank is equipped with an electric backup coil but I have never hooked it up. If I run direct, I can leave the boiler and controls powered down all summer, it saved me a about a gallon of oil per day. I actually have a solar powered circulator pump so there is no electric load for hot water except for my water pump for 5 months per year
Do note there are two types of systems, evacuated tubes and flat plates, evac tubes put out hotter water but less of it while flat plates but out more water but at lower temp. If you want to integrate the SHW with storage, evac tubes would work better as flat plates only raise the water temp over the outside temp by about 80 F max while evacs are more like 180 degrees. Evacs cost a lot more and you need to have a fool proof way to dump the heat in the summer.
The panels are roughly 4x 8 and should be mounted at your latitude plus 15 degrees (I.E I am at 45 degrees lat so my panels are tilted at 60 degrees. Unfortunately that rarly lines up with the roof pitch so they can be ugly. If you drop them to typical roof pitch they wont work as well in the winter, plus will tend to build up snow and will overheat in summer.
Rigging them in place is a two person job preferably with a crane. I built a derick out of 2x4's and used pulleys and come alongs. Whatever you do make sure you have someone who knows roofing to install roof boots for pentrations and flash all the points that the panels are attached to the roof. The piping is pretty straighforward, the biggest hassle is finding a charge pump to charge up the system (I bought one from Northern Freight).