[TYPO3] Hooked functions for fe-registration available?

[Niels Fröhling]

Hy;

I'm going to implement a extranet containing website in short time and 
would like to ask for advice how to 'adjust' the registration-process in 
a non-offensive way.
The procedure to implement is roughly this:

- registration with custom data-aquisition
- creation of up/download space (possibly to be moved into a 
confirmation post-process)
- confirmation-procedure with the new user
- notification of an administrator
- possibly a "accepted" action/notification through administrator action

I'm almost sure I have to write a custom extension anyway, because I 
can't offer the standard user-management interface.
The fe-users is given a communication-platform with the administrator(s) 
or assigned maintainer(s). I hope I don't have to implement fine-grained 
access-control, but I should prepare for that. The communication 
consists of messages and files, which can be up/downloaded from both 
sides (this is where I see the unevitability of a custom extension, 
which integrates a communication-management module). I see a big 
logistic problem with handling files, as file-handling is spread over 3 
or more modules. Having just a different view would suffice allready, if 
the programatic maintenance of all the related data isn't too fragile 
(like auto file-list contents with access-restriction), even though I 
see an advantage to just offer a distinct 'view', but preserving the 
'standard' data-organization in the form of content-elements, as they 
stay manipulatable through standard-views.

I hope to receive some suggestions on:

- how to inject a custom form into the registration-process
- how to hook a function (or if possible 'scripted actions') into the 
various steps of the registration
- if there is a possibility to generally maintain db-driven forms 
without programming any code (FLEX?)
- if there is an API for custom access hierarchies (principly N:N, I 
hope I can evade it and do only1:N)
- if there is an API for be-list generation (the list-module) for custom 
entries, if possible for the be-list tree too
- how to handle files in this context

I'm not expecting detailed how-tos, I just want to be guided by your 
opinion and experience. I'll figure out the programation. :-)
If finished, and not very crude, the code goes back to the comunity.
Thanks
    Niels