1) Yes, of course you can. There are multiple Portal Addons, just check the Resources tab here 
(http://xenforo.com/community/resources/simple-portal.1713/, http://xenforo.com/community/resources/8wayrun-com-xenporta-portal.90/)
You can work your way to a nice Software Product Homepage that way.
2) Again, check the Resource Manager 
(http://xenforo.com/community/resources/donation-manager.385/)
It's by default in the sidebar, but it can be placed above the Users-Alerts-Inbox if you'd like it too.
3) Yes, that can be done. There also is a download counter. You can specify yourself what a non-logged in user can do.
4) That's not possible yet, but I'm sure it can be created by one of the developers here on XenForo.com
5) You can try out a demo at http://xenforo.com/demo/, but you can't do a test import.. I can assure you that (almost) everything will work, since it has been done sooo many times
If you have any more questions, feel free to ask!
