Hi Bill,, Yes I think the EFM 520 would be the right size for your application... and since you plan on burning coal year round to heat DHW, you could continue to use the coil in the oil boiler, or get the EFM with a water coil..
You will need a circulator between the two boilers... or if you use a DHW coil in the EFM you could use manual isolation valves to shut off the oil boiler in the summer, You have lots of options..
Since you will be moving the existing boiler, and have to replumb a lot of it.. you can almost start from scratch with the design of the system,, use of the two boilers, or only one, etc.
About your circulator pumps.. what are they?? The common B&G red, motor/connector/oil bath/pump circulators.. The B&G 100 model? or are they the more modern cartridge circulators? in the zone where you have a cool room at the end of the zone,, a slightly larger pump would be a LOT less expensive than one of the automaticly variable ones.. There are several pumps with a manual three speed selector switch available from Grundfos.. the 15-58, and 26-96 I think I have those numbers correct, these pumps come as single and three speed models. With a three speed, you could manually pick a faster speed/higher volume for the zone and see if that fixes the cooler room.. You can buy these circulators on Ebay for a good price.. just get the retail and decide how much you want to pay.. I've bought the 26-96 single speed for $80 shipped off ebay,, they are a $250 pump..
Check out some of the threads about hooking boilers in series vs parallel vs primary/secodary.. PM forum member 'sting' and get the titles/publisher for the books he recommends on boiler plumbing,, or find them at your library.. and read up, You have an opportunity to plumb a really neat system..