Plugins with WordpressMU

I am new to the forum and the information is great but I am getting information overload. I am in the process of setting up WPMU in a folder in my main website in order to setup about 100 or so subdomain blogs. Does each blog formed under WPMU have it's own plugins or do they all operate under an umbrella of plugins? What I am trying to accomplish is to have some feed by the rss feed from my articles directory with a rewriter, some feed by other content generators like CC, etc based on the keyword. Any suggestions?

It depends. If you put the plugins in the wpmuplugins folder then the plugins will be automatically active for all your blogs. If you put them in the "normal" wp-content/plugins" folder then you can enable/disable them on a per blog basis. Note that lots of plugins won't work right in the wpmuplugins folder; that's why the wmpu dev folks have the premium section of their site.

So since I plan on adding them slowly anyway, would I be better off just setting up 2-3 manually a day until I decide I have all I need?

well, what could be extremely interesting for you is the donncha domain mapper plugin - each subdomain can me mapped to an individual domain. you don't even have to add them in the admin interface but write a quick sql insert. 1$ on godaddy for a .info and no fear to get deindexed making all your work useless: this is worth the investment.

good point and something I should consider. My host allows unlimited domains so it is an option.