Thats alot of wood to feed with all the btu's you need.Will you be using wood and coal,the coal will be much easier to control the boiler temps. Do you have a wood supply for all those btu's needed.
With using wood it seems to have heat spikes when fire dies down then oil burner kicks on untill you load with wood again,and again, and again,its a visicous cycle.I have watched my freind do it with his boiler.
Not sure about 9 gals. of water for 300k btu's.
The woc100 will surely do what you need at 400k btu's with some extra to spare.I have noticed that with all the amount of coal in the fire box,it seems to keep the boiler temps. 170*/180* without a problem.
The 5gal. DHW coil makes temendous amounts of hot water.If you need more hot water there is a 7 gal. coil avalible.
I have mine on the coal/wood only,I shut off the oil completly and you won't need oil at unless you go away for more than a day.I don't even know how to use the auto switch over,I believe I should learn before needing it.
AHS really built a soild multi fuel boiler
.Since I bought mine I been looking really close to all the other multi fuel boilers, and the others don't seem to burn coal very effectivly, but will burn wood with out a problem.
If you have any other questions or want any pics. just ask. Dennis