Welcome to CHR! I won't try to add more details, but I will echo what's been said about choosing your rear end ratio. Decide on the tires you're going to run, confirm your 700R4 OD ratio (likely 0.69), and select your cam to give you a fairly flat torque curve. With your tire OD you can run the numbers to find rear gears that at highway cruise speed sets your RPM towards the bottom of the flat part of your torque curve for good economy.
When I was doing my coupe (Tremec 5 speed), 30" tall tires) the tranny guy suggested 4.11 gears and I told him he was crazy, I wanted a highway car, not a drag racer. He told me to run the numbers, I'd be turning 1995rpm at 70, and getting up to 70 would be like a rocket! On my Ford 347 (302 bored & stroked) my torque curve is steep from 0 to 1800, starts flattening to about 2000 and stays there until it rolls over at about 5800 to 6000.

Good luck on your build. Glad to have you here, and we LOVE pictures of the build process!!