I just did this job. If you do a search on my user name...you should find my thread on the subject with some helpful hints from other people. Overall, the job was super simple...even I completed it by myself.
http://forums.pelicanparts.com/porsche-911-technical-forum/643565-dead-brake-pedal.html
As for your question, no...don't disconnect teh master cylinder. You should be able to unbolt it from the frame of the pedal cluster and slide it out in tact. Draining and bleeding would be additional work that isn't needed.
As far as bronze bushings...can't answer that...but I'm not sure it applies to G50s. I bought a used cluster that was already cleaned and such. I tried to get one person to rebuild it...but I ran into the problem of the spring that needed replaced no longer being available.