There are getting to be so many great methods and materials for dry plate photography you're sure to find one that fits your style of working. You're going to have a blast!
As for your other question about plate holders, there's ebay of course, but I've been noticing that holders aren't as easy to find or cheap as they were just recently (that might be a cyclical thing.) Fortunately, you can easily make your own plate holders from old wooden film holders, which seem to come available regularly. Here's a bit of info on the 'how-to'. Mostly, it's pretty straightforward intuition. http://www.thelightfarm.com/Map/DryP...PlatePart6.htm
Best of luck and fun,