Sorry you got stuck with that, maybe you can have your step dad call our resident RO guy to help understand the needs of your tank. You could ask your step dad if he simply wanted to be able to make water with it and If that is the case, all RO/DI units can do that, you just put a valve before the DI and Home Depot sells the water tank. We can help step you/him through setting it up for that, no problem. The RO you got is for drinking water, not a tank. Will it work? Sure, but you are very likely to have tons of issues that will make this a lot more difficult, and not nearly as fun, because the water will have a higher TDS than you want brand new. For example, i replace my filters when my water measures 5TDS, the best this RO unit can produce is 5TDS water, so out of the gate i wouldnt use it in my tank.
The water quality is the number one most important thing in our tanks, and you are doomed to fail if you start with bad water. I apologize if i sound like a downer here, just dont want you to lose all your enthusiasm for this great hobby because you get started and have algae breakouts all the time or cant keep corals alive. It is so important in fact, that just yesterday at our club meeting we had an hour long presentation over RO units to make sure veryone understood the role they play. If you cant get a better RO unit out of him, maybe you can at least get an addon DI stage, that would help you tremendously - http://www.melevsreef.com/shop/diadd.html
As for salt, people will debate it all day which is best, id just grab whatever your LFS has when you go to town. It might matter more down the road if you get SPS corals, but right now it wont. Franks Tanks or True Percula on your side of things will have what you need, so give one of them a call, franks is closed on sundays btw. Just as a note, Home Depot salt will not work, just in case your step dad gets any ideas because a bucket of salt at a LFS costs like 60-70 bucks and he wants to try something else.