I used a storage tank for about 10 years with an old MeMCo boiler. I am now using it without the tank waiting for my Keystoker. My tank was an old propane pig that held about 365? gallons. The boiler held an additional 50 gal. The difference I am seeing is that when the temp drops quickly I have no buffer if I am not right there to add wood. But on the other hand I can get a fire going and quickly get the boiler up to temp. I am not using coal this winter as I have purchased 11.5 tons of rice coal and it wil not work well in the MemCo.
If I had to do it over again with a wood boiler and a storage tank, I would have to have at least 1000 gal. of storage and I would have it set up as a low pressure system with a heat exchanging coil. I would build my own tank and super insulate it. You have prehaps the best boiler for burning wood I can think of and it will work best as most wood boilers do when it is running flat out. This is where the storage tank is great. Without it the system has to idle waiting for the house to call for heat and there is a lag time for it to respond.
The only other thing I would say is that it is frustating to have all that water at say 160 degrees and it will not heat your house worth a damn. Unless you have radiant heat. Baseboard, old radiators, and any other types of exchangers just will not work unless the water is getting up around 180. For this reason I had my high limit set at 210 before it started dumping heat to my dump zone. This is much higher then anyone will recommend and it is hard on the system. I was maintaining it myself so it was my problem to deal with. But I must say, when that 210 degree water hits the baseboard it heats right now!
There are other things but this is already a long winded post. If you have any specific questions about my comments, just ask. Glad to discuss it.