After many hours of research, I've answered some of my questions I mentioned in Hydronic System Planning, so it is time for an update.

Did I miss anything? :-)

Yes. since I plan to isolate the house sytem from the engine system, a coolant expansion tank is needed. The expanstion tank cap will be the highest point in the system. It is the kind of tank that is pressurized (7PSI). If the system is too full or boils over, the capp will open and release coolant out the vent hole. It can be run out of the van or into an overflow tank. Overflow tank is nice if you don't want evey spill coolant on the earth or fear you migth overfill. But it is not necessary in our application.

3 Way Valve Control

Can the the EastStart Pro control the Eberspächer 3-way valve so I can run the coolant pump and circulant coolant through the plate heat exchanger? I believe residual heat mode will run the pump, but I’m not sure about the valve.

No. The EasyStart Pro only connects to and controls the furnace. It can not control the Silencio 2 (air matrix \ radiator) or the valve.

Further, the Eberspächer valve is an automated valve, not a relay controlled valve. It is not suitable for this use case, where we want to control water flow to our preferences.

Can also add the EasyStart Web to the system?

Yes. But Not in the U.S. This controller has its own builtin in LTE connectivity. It is only available in certain countries.

Silencio Contoller

I’ve looked through the EasyStart Pro Installation, Instruction and Wiring diagrams. I don’t see how the EasyStart Pro wires up and how it controls the Silencio 2.

Sadly, it does not also control the Silencio 2, or any air matrix \ radiator fans. This is very disappointing as it means having to controllers. Seems like a real miss. In an Air heater solution, the Pro will control the whole system, this limitation is only for the hydronic heater.