1. Put the "fixture" valve right at the tee and run 1/4" copper to the icemaker. Do not worry about the pressure, 1/4" copper is stronger than 1/2".
2. Unless you have a gas leak, and that would be a major problem, there is no more danger to using a torch around a gas water heater than anywhere else, as long as you do not set the building on fire.
3. I does not matter where you install the tee. By the time the water reaches the icemaker it will be the same temperature as the air in the room. In fact, sometimes connecting to the hot water side will give clearer ice cubes, but you might not want to experiment.