I always keep the suction pressure from the last sytem I worked on in my hoses and manifold; I drain the high side back into the system through the low side so whatever that pressure is stays in the gauges.
As far as bleding the 6" extension, I use valve core depressors a lot of the time, so when I attach the hose to the depressor I can bled some of the pressure from the gauges at the depressor. This also saves freon burns in those tight places.
I don't have half the experience of many of you, but I actually use NRP low loss fittings and YJ ball valves. I trust the ball valves a lot more. I read somewhere that someone didn't recommend leaving your manifold full of gas. It slowly stresses out the hoses or something.