Starting fresh with A/C system. Pressures too high

[ps2cho]

I want to tackle my A/C again in the next month or so.
In short, my pressures are too high. 105F Ambient is 55psi / 340psi at 2000rpm. And please, before anybody states it, I am not overcharged. --Anything over 16oz of R134a put me over 300psi.

Q1: Whats the most efficient way to FULLY flush the system to ensure I am starting with a clean slate? Can I flush the evaporator safely once I remove the expansion valve? I have A/C Flush solvent and a compressor. Once I run it through and use the compressor to blow it all out clean, how long should I wait to ensure its completely evaporated off?

Q2: I've only ever vacuumed down for 15-20mins. How "long" is long enough to ensure 100% boil-off of any air in the system so I am 100% sure I have a full vacuum throughout?

Parts I will replace:
Compressor (as I have a brand new Denso one ready)
Expansion Valve
Drier
Main A/C hose (as its leaking slightly).