Build a bench that is equal to the height of the door sill. Cut one end so it is at about a 30 degree angle to the driver's side. That way, when you're lying on your back, working in the driver's footwell, it is a lot more comfortable. Search here and at http://www.classiczcars.com for information/advice. It's out there, and it helped me. Read the FSM. There is a lot of good information ready for your consumption.
What Blue is trying to tell you sans words free is that you will notice a higher or eratic idle with the brake pedal depressed when you are stopped. There will also be an audible hissing sound of air entering vacuum along with more brake pedal effort to stop. Its usually the diaphram that goes over time. Changing out the booster is a simple job. Took me about a half hour when I did it on my 240. Remove the vacuum hose, unbolt the master cylinder from the booster & unbolt & remove the booster. You don't have to remove the brake lines from the master cylinder. Just move the MC slightly out of the way so the booster can clear....but be carefull not to bend the brake lines. You might also have to play with the plunger rod (no pun intended) & the brake pedal to clear taken the booster out this way. Installation is reverse.