1. I use a plastic clothes pin on the middle V part, and it keeps the film separated when doing 4x5's. Just like in this web page here: http://www.largeformatphotography.info/unicolor/
2. I live in a pretty dry climate, but don't really seem to have this problem. I do load my film in a changing bag, I'm not sure if that hurts or helps, though. I use my bathroom as a darkroom, and usually run a little hot water or take a hot shower before doing anything with film. Make sure your film holders are clean as well, and that there's not a lot of dust floating around your bellows!
3. I've seen this before once or twice, and I'm pretty sure you're getting this because of the film touching another piece of film.
4. Probably you just need to be a little more careful. I've noticed, however, that some films seem to scratch a little more than others, for me anyways. Maybe it's just me being clumsy.
If I can be of any more help, let me know!