need help setting up media agency

hi, so im a little confused, here is what i would like to do.

1. im creating an online media agency (umbrella site) that offers;
-- SEO
-- graphic design
-- web design
-- video
-- photography
-- tuts

2. however for all these sub sites, i will be recruiting people for each task, i have one theme that needs to be installed for all, and ideally i need all the sites integrated (multisite..do you recommend it for this situation?)

3. is it possible to link up certain plugins such as "appointment plugin" for all the sites?

4. is there a plugin that all these sites can use that tracks orders and client to the developer (so the umbrella site can keep track of whats happening etc)

5. do you offer install and setup of need plugins if i pay?

6. main concern is tracking all orders though me, so i would need a way of having a funnel from user to "sub blog" owner.

really hope you can help me!