I'm venturing a few hundred years out of my comfort zone (15th century) here, so please bear with me.

My reenactment team is looking for opportunities to go multiperiod, and of all the options we discussed, Great War reenactment was the most fascinating to us, so it's up to me to have a look at the basics and see what we can achieve. If we are going to do something, we'd like to do it right.

We would like to start a Great War cavalry unit, preferably something based on a continent unit (we're actually considering to portray Germans - or is that not done?)
I'm bascially looking for some good sources for information (books/websites/videos) and for vendors (preferably online) who sell the neccesary equipment.