The clutch on my AC compressor bit the dust under the duress of Central Texas 100+ degree heat.

I found a decent price on a new, after market compressor made by Global AC CO. and it's on the way along with a new drier/accumulator. I plan on removing the old compressor and drier and installing the new pieces, then taking the car to my my trusted mech. and have them give it an R12 charge and test the system for leaks.

AC systems scare me a bit, so in attempting the repair my questions are:

Before I crack open any lines to remove the old compressor, do I have to evacuate the pressure somehow and if so, how do I do this?

Is there anything else I should check and consider replacing (accessory bushings, pressure lines, etc...) since I'm working on the system and that would make sense for the longevity of this system repair?

Is there anything I should be aware of regarding an after market compressor opposed to considering a genuine Volvo?

Lastly, is there anything I'm forgetting in order to "prep" the car before I take it to the mechanic? I want to make sure I do everything I can to make their work quick and hopefully inexpensive!

Thanks in advance,
Jason