User specific pages

I’ve had a request to add the following functionality to a site I’m developing, and I haven’t come across a plugin that does exactly what I want. The brief is as follows:

A staff login that will go to an individual page for the staff user that will display a calendar of work shifts, and the ability to book designated training courses.

A client login that will allow them to book a service, and pay bills on line.

Would it be easier for these to go to an install on a sub domain of the main site, or is it possible or even desirable to keep this all on the one domain?

Cheers
Mark