You do have to run a return from the engine to the tank. The fuel pressure regulator controls pressure by regulating flow returning to the tank. Meaning that the line runs from the tank to the pump, pump to the rails, through the rails, through the regulator (just a restriction to build pressure), and then back to the tank.
As far as where to mount an inline pump, you would have to be below the tank. You can use a pickup style feed line like your carb pump uses, the line goes in the top of the tank and extends to the bottom of the tank. Problem here is if the fuel is low and sloshing arround, you may lose the siphon and that could cause problems. I think the best bet is gravity feed. Again, mount the pump below the tank, then put the pickup for the pump at the bottom of the tank or even better is build a sump for the bottom of the tank and put the pick up there. The best location is at the back of the tank because fuel will slosh back when you accelerate and that would put the fuel right over the pickup. For the gravity feed system, the feed line from the tank to the pump should be bigger than the line from the pump to the rail. This gives the pump an extra supply of fuel to draw from and reduce starvation problems at the pump.
I've got a good fuel system basics article (from a car magizine) that I could scan and email to you if you are interested.