Greg, you can go to either
www.keirinponds.com or to
www.yumekoi.com for all that info. The trays in inches are about 10"x10"x30". A four tier shower holds 50-60kg of media. The flow rate for one shower is supposed to be between 3000-4000 gph. If you live in the states you might want to give Keirin a call. They are really nice folks and will answer any questions you have. They might even know of someone in your area with one so you can check it out, or have a dealer near you already.
If you tell us more about your gallonage, conditions, and fish load we can ask either Carl from Keirin or Mike Snaden from Yume to give us their opinion of how much media you should use. Since ponds really vary with stocking rates, the 2000 gallons for one tier does allow some breathing room for the normal overstocking most folks with a pond that size do.
Bob Hart who just posted here has obviously had some experience working with it, and looking at the fact he is buying more I would say he is probably pretty satisfied with it. He might be able to tell you more about his experience.