I am replacing my electric stove with a gas stove... Off the 1 1/2" main line in the basement there is a tee, elbow and 3/4" plug, I plan on running the 3/4" black pipe over approx 1 ft, 90deg elbow 8 ft' run and 1' up through the floor, shut off valve, and flex line to the stove. Other appliances are gas water heater and gas boiler down line. Anybody see any problems with this layout? Although I have work with pipe in compressed air and water applications, this will be my first attempt at a gas line. Any pointers would be great... Thanks in advance!

No problem here. 1 1/2" existing gas line is large enough to carry the stove w/o problem. Install the connection as you described. Don't forget to install dedicated gas valve behind the stove.