Please see comments below ...

xavierhoughton wrote: I have a specific registration requirement for subsciptions.

Restrict access to full content (not preview/intro) in multiple catergories

Yes, CBSubs can do this on a plan/subscription basis.

Subsciption 1
Simple signup 7 day free access - email and name only with random password generated in the back end.
Email allert upon signup promting for upsel subsciption (subscipton 2)

Users need to be website users to sign-up for a plan.
So plans can be presented on the CB registration form.
CB and Joomla need minimum info for registration.
Username, Name, Email and password fields are needed.

Password generation can be done in CB (CB feature you can explore on your own).

You can have a CBSubs plan that is free for 7 days just fine.

Subsciption 2
90 day free trial to content and magazine.
Signup to include full name and adress details.

Yes for plan duration and cost.
See previous comments.

Subsciption 3
Anual access to content - paid

is this possible?

Yes for plan duration and cost and access to protected content.