hmm i'm not really an expert, because i didn't have a ubb before so i can't say how the importer works, but i try to give some of the answers, perhaps others can answer the rest
1. As i know there are know problems for this
2. I think you have to move to the new server before, but perhaps there's also a script somewhere, which doesn't need it.
3. Most of the changes are structurechanges to the DB i know, so it wouldn't take too much time
4. Hmm, don't think theres an access before you buy...
5. it'll delete most of the data which was hacked in an ubb, if you have an unhacked ubb, i think everything is converted
6. uo, i really don't know, but i think yes vb has to be installed
7. no, the installscript makes everything you need, you jsut have to enter the dbname, server and pw
8. yes you can change there usergroup to need email validation and sent out an email then

9. don't know, on i haven't had any problem with email features till now
10. just german ones ^^
11. if your server is too slow, you can get whitepages sometime if you move... a thread
12. no it's one of the easiest and safest boards you know
hope this could help, but if anyone cann add, please do