You don’t mention which version of After Effects you are running, nor whether you have a multicore processor.
After Effects 7 only sees 2 GB of RAM. CS3 sees 3 GB but if you enable multiprocesssing it can use all available memory, you need at least 1 GB per core.
If you have a multicore machine try Nucleo Pro to speed renders. You can download a trial version from their site to see whether it helps.
There are many methods that can work. Duplicate the layer. Mask your subject out on the top layer. Remove the color on the bottom layer by one of several methods. EG use Hue Saturation on the layer and remove the color. Use Channel Mixer to remove color etc
I have a Mackie 1202 VLZ and mixture of lectrosonic and sennheiser lavs.
I’ve just learned there will be audience Q&A as well… so now I have 7 audio sources. I plan to put a mic on a stand for the audience (come to the mic to ask a question) and have a wireless shotgun on a boom with for those that won’t come to the mic.
I’ve added another camera just for audio, that gives me 6 audio inputs.. something will have to go through a mixer.