TXDave,
4-strokes fool a lot of people, so don't worry about it. There are only 2 parts of the fuel system. The fuel intake at the carb goes to the pickup line on your tank, and the muffler pressure tap goes to the vent line for the tank. The third nipple that you mentioned is the crankcase drain. It allows excess oil to drain out of the crankcase. Hook up a small piece of tubing to this nipple and route that outside the engine cowl or fuselage so it can drain out of the engine without building up inside the fuselage.

As for other things to worry about there are a few to take into account. Oil content in your fuel needs to be 18% or higher. Other than that you can use just about any fuel you want to, you can even use the same fuel that you use in your two stroke engines. I use Cool Power 15% in everything that I fly (both 2 and 4-stroke) with no problems. The other thing that you'll need to worry about it the valve clearance, make sure that it's set properly. I looked on OS's website but couldn't find a manual for the 48, but here is a link to the 52 Surpass
4-stroke. [link]http://osengines.com/manuals/fs-52s-manual.pdf[/link]Setting the valves should be similar for both engines so you can use this as a guide.

Hope this helps

Ken