We already have a very flexible membership management system which we can customise for you. It features a number of robust modules from Membership Management, Subscription Management, Communications Management (Bulk Email, Mail Merge, SMS - platform dependant), Reports, Member Demographics - setup unlimited fully customisable heirarchical groups. There is an option for Document Management as well (separate system, but with existing integration modules.
I am sure we can easily customise this system to suit your needs. We can give you a demo of this system at any time.