Which Plugins should I use ??

Hi Guys,

I am looking to try and figure out the best plugins to use for my new Website, it is basically a Multisite install using BuddyPress.. that allows my members to sign up and add their own blogs (Similar to Edublogs but Fitness Related) Most of this will be free with an option to charge for premium add-ons and domain names etc.

Looking through all the plugins available I am really confused as which ones are best to use and a few seem to offer similar functionality??

Are there any that don't work well together?

Also is there a recommended limit on the number of plugins to use on one install?

Sorry for the long question... just eager to get started but want to make sure I make the right decisions from Day 1...

Kind Regards