1. You can only upload a file up to your max php upload filesize set in php
2. I guess that would depend on vbadvanced CMPS. I dont use that product so I can not answer. I know to get vbadvanced to work on non vbulletin pages requires hacking. vbportal works out of the box with either product.
3. If you create a forum that is merely a link in your vb
admin cats editor sure. Thats a default feature of vb
there is a box in there that specifies whether it is a forum or a link to an external app.