Don't use threaded PVC, it is very easy to over-tighten as well as under-tighten. When you glue pvc together the glue actually fuses the two fittings together, basically making them as one. It is "almost" impossible to remove a fitting that has been glued, which is a good thing, it shouldn't leak. The only places where you should use threaded fitting is the bulkhead itself and maybe the fittings connected to the bulkhead. You can also use barbed fittings with durably braided/poly hoses and use stainless steel pipe clamp out of the water, and you can get plastic pipe clamps for underwater applications.
As far as housing SPS/LPS you will need a mature tank especially for SPS. I would wait atleast 3-6 months (I am sure others can chime in if I am wrong). Hammers, frogspawns, torches are good LPS corals to start with. As far as SPS, I am not sure if there is such thing as an "easy" coral. I believe that Montipora's are a little more flexible.
You will also have to concider how you plan on dosing the tank for calcium/alkalinity. A calc. reactor is a wise investment but they can be spendy and won't be needed until you have heavy bio-load. On my 55gallon with 10 SPS I am using two-part and am having a tough time keeping my calcium levels up.