The 46AX is a great engine for this plane and you will be at 1/2 throttle a large part of the time.

Yes, you can use a 3-line fuel system. Connect a line to the third tube coming out of the tank for filling. You'll need to plug the line while running the engine.
Inside the tank you will want another line with a second "clunk" on it. This is needed to defuel the plane.
You don't want to fill between the needle valve and the tank or between the carb and needle valve. Either point would result in a flooded engine unless you clamp off the line to the carb or needle valve.
I prefer to have the antenna come out the top as it will not snag on things so easily(grass, branches, etc).