1. There is no itrader import script that I have seen. We typically do not create importers for vb hacks/mods.
2. Fees to list are per category not usergroup. So you can have different listing fees for each category so if you have a category called cameras you could charge 2.00 to place an ad as an example and the next category say called Computers you could charge 5.00 to place an ad.
3 and 4. Yes Our subscriptions work kind of the same as vb. You can setup flat fees to post in a category for ads as noted above in number 2. You control over which groups have to pay or not through usergroup permissions. As far as subscriptions like vb you can charge a fee or many different fees to put a user into higher usergroups which may not have to pay the listing or have permissions to more categories etc etc. There are various different ways you can set things all depends on what your doing.
5. No. The forum is the forum and classifieds is the classifieds totally separate applications like photopost and reviewpost we use the forum header footer style. If you use our other applications and like them you should be familiar with how things work.