Here's the pipe assembly dry-fitted, in the orientation it will be under the floor. The standard method for installing rigid pipe like this is to start at the fixed starting point (that capped nipple) then add one piece at a time, working your way to the destination, in this case the oven at the end of the brass valve in this picture. It will start with the 90 elbow on the left, long pipe 90, short pipe, 90, medium pipe, tee, medium up, valve, tee-short down, cap. Easy, right?!
A triptych of the iron pipe where it will be installed in the basement, and one glamour shot of the valve where it will live behind the stove, if I live through the install.