The upload from usercp part would defentaly require a hack, currently attachments are assigned to a postid when uploaded via posting, and altho they can exists without a postid there is no way currently to re-assing one when posting.
So you are looking at adding some php to upload from the usercp, adding some php to re-asign a postid when posting, and bulding a template to contain it all.
We don't deal with hacking here so you would have to ask at vBulletin.org
The quota thing may be possible via template modification, I will look into later