the rawhide will protect the back and should be done after heat treating so the glue will not separate. heat treating will make a stiffer bow, so it will be slightly thinner, but it will not make it stronger or keep it from breaking sooner. getting the wood too dry by heat treating actually might make it break sooner than if not heat treated. It is often used to gain a few pounds if coming in underweight at full draw.
as you get closer to 28" with your 30# goal, you should be looking for signs of early set taking. if that happens, you have to go thinner to avoid excessive set at 28" and maybe come in light and should at that time consider if you need to heat treat.
I guess some folks like to consider it a step to making every bow, but if it is not necessary, why bother? do you live in an excessively humid area?