Lewis,
I would guess (could be wrong) that the number stamped on the rotor is the minimum spec. I would expect to see a service spec in a service manual. Common practice in the industry is to stamp minimums.
If you are at the minimum or just slightly above it I would replace the rotors. It is always a good idea to at least resurface the rotors (turn) when fitting new pads. If you do not have a brake vibration before needing the pads you could get away without turning them. Just be aware that your pads will take afew stops before they are at full effectiveness.
Personally, I prefer to change rotors every pad change. Most people do not. I believe BMW reccomends this as a normal practice on their cars. You certainly do not want to run rotors that are under the min spec. I would also not fit new pads to rotors that are at the minimum. The pads will wear the rotors below the minimum and you could loose some braking effectiveness.
My advice is to turn them if they are safely above spec, the shop doing the work is normally qualified to make that call, and fit new pads. If you are on the borderline for thickness, splurge for the new rotors. Unless you have a bunch of miles on the rears are most likely fine. Fronts wear from 2-4 times faster than rears.
Good luck
Oops, almost forgot the bleeder question
I have a power bleeder. I pump mine up to 10 psi, that is what the manufacturer of the bleeder reccomends. There are also bleeders that use tire pressure which is obviously more than 10 psi. So I would not worry about doing and damage to the system. I think the lower pressure probably causes a little less aeration of the new fluid, which will cause a soft pedal. Answer is, 10-15 psi. Works great on all of my cars.