if I'm not mistaken, you can perform the following steps :
To control how many files are allowed for all user: Click Manage Plugin or open URL yoursite/admin/plugins...then ...
Setting Photo Plugin or open URL yoursite/admin/photo (Options: Upload Settings, Limits, View Settings, etc) -> Click Save
Forum Plugin Setting or open URL yoursite/admin/plugins/forum (2 options: Enable file attachments
and Attachment maximum file size)..
But
also set the mailbox plugin,
U cant add an extra field to the user profile but youcan add some of the things required in the profile page: open yoursite/admin
-> Click Users -> Profile Questions or open this URL
yoursite/admin/questions/index in your browser..
click Add Question...answer type->extended text (user can add long text)