specific use case - need some help

Hello everyone,

I've been cracking my head trying to figure out the best solution for a specific need I'm having, but with no success. So I'm posting this to get some advices or helpful ideas.

I'm part of a center which develops several activities in the field of health and personal development. Our website is been running on Drupal, basically just to manage events, basic user registration and sending of newsletters.
With the growth we have been having and our current needs, we need to expand our website to have a more complex contact management.

Just to cut a long story short, this are our main needs:
* contact database with personal info
* link contacts to activities or events they participated in
* register payments (linked to contacts and events)
* being able to group contacts by classes, and keep them after they are over
* send emails/newsletters to specific groups
* able to track and notify of missing payments

and a bit more complex:
* book events to rooms (dont allow the same room to be booked at the same time)
* allow participants of some classes to access online materials (files)

The first thing I thought was to use drupal+civicrm.
Since I'm not the one who is going to be using it, I'm not sure if the complexity of this solution would be too big for its users.
Also, so far I could not get a simple way of solving the last 2 needs using Drupal.

Of course the ideal solution was to develop the system myself, but that would most likely take me a couple of months :-/

I appreciate any suggestion you can give me.

Thanks
Nuno