Free Shell Server setup/PHP script for site.

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I'd like to enable free shells for users who sign up for my site.
I run a NetBSD and Debian server. I'd like to offer these things:

1 background process.
5 processes. (I know how to set this limitation by group/user.)
E-mail (automatic)
FTP (Automatic)
Typical things to allow users to access the *nix environment remotely.

Most importantly, space is an issue. I'd like to assign each user 1MB of space that dynamically expands to 10MB based on their data usage.
IE: If they upload 1MB, a script detects this and extends their /directory limit by 1 additional MB.
This would save space for users who will only load a BNC or GCC a few KB files rather than giving them 10MB of static space.
I'm not sure if this is possible.

The next and most important feature is that I'd like my registration script on the website to add their account to the server automatically after site registration is completed.

If anyone has any tips - documentation or knowledge please let me know.
Thanks ahead of time for your comments and replies.