I haven't used the v2, but I have used sugarpeas snapins many many years ago (assuming it is the same design?).. The thing I didn't like about the wool in ones is that if the poo gets off the snap in, then you have to handwash the wool, and I never mastered this skill.. wool can bleed its color, plus it also takes a long time to dry. If you have a lot of them, that probably wouldn't bother you so much, but I would get a few of this and a few of that, and so I was always waiting on one part or another.. I thought the mediums fit my kids well, but the large sizes had a huge rise on my kids and never fit them well (but if you have tall toddlers it might be a perfect fit).
Yes, you can use prefolds in pocket diapers. I did it all the time. Sometimes you need a smaller size prefold to fit properly in the pocket of a larger pocket diaper. (So infant size prefold folded in a large pocket for example).