Cyber36, see http://www.hilkoil.com
As far as tempering valves go, unless you have the more expensive Honeywell-Sparco or Taco, you will need a throttling valve to control the cold supply to the tempering valve.(read watts 70A) You will get too cool of a water supply elsewise. The 520 EFM has very good hot water production if set-up properly. This includes coil/valve piping and boiler or system by-pass if a high water content system is connected.(read C.I radiators or radiant slab)
A coil booster tank is a good thing, but I'm not too crazy about hearing them hooked up without a bronze/stainless steel pump in-line.