It is pretty simple, actually. And it can be even simpler if you don't need all your fittings on the bottom of the tank. For example, it's completely kosher to route the oil return line just to the top of the tank or a high point on one side. For the next one I build, I think I'll try a vented cap, so I won't need a visible vent line.
There's a million ways to skin this oil tank cat, and I'd say you're off to a good start by thinking about every aspect and asking lots of questions.
Cheers!