1. IPB2 support is included in the current release.
2. We're considering paid subscription levels; however, ones that work with integrated forums are a bit more complex.
3. We have http://www.photopostdev.com
but have never had much of a community for offering skins. We even offered a contest that paid out hundreds of dollars and only had about 6-7 submissions.
4. We havent considered a top sites version, but will keep it in mind. We have a big upgrade in progress for Classifieds.