1. You can not convert the license purchased elsewhere to a full Pro license. There was a deal years ago when the licenses where first transferred but that expired years ago. You would have to purchase a new license if you wanted to convert this one.
2. Your main license where you have access to Pro you can renew there is no need to buy a new license there. Now if you own multiple licenses and you only have one active install you could theoretically use that second license on your vbgallery. However if your using both licenses on different sites you would need to follow the advise in number 1.
3. There is a vbgallery to pro import script which works in the pro import forum. I just used it recently to convert a customer.
4. vb5 is an internally developed alpha to my knowledge. We do plan to integrate with vb5 once that script becomes available to beta testers and we have access but if the process is as difficult as it was to get access like in vb4 we could not say when we would officially support such a forum. I remember back with vb4 we officially got access to that code like 2 months before vb4 went gold. Definately not a friendly process for developers trying to make there scripts compatible with the product.
Our products are compatible with the vb
4.2 series with lots of enhancements over earlier versions of our software.