As the politicians say, all good questions. You are planning for storage. To me that means you want the ability to let your WG burn full out, one or more loads of wood, and then burn out. You will use your storage to buffer (accept the excess) WG output when your system does not need all the btuh's, and you want to store btu's for later drawdown and not always burn the WG, perhaps have several hours to overnight (or longer) of btu's available between firings. You also may want DHW, relying on the stored btu's, especially in the non-heating season, to provide that, and only have occasional firings of the WG. Lastly, you would aim for minimal to no idling with the WG during its burn times.
A question you didn't ask is how high a temperature of water do you want to be able to achieve in storage, and related to that is what is the temperature demand of your system. The lower either of these are, the easier it is to plumb and choose a circulator to meet your needs, and the opposite is also true, that the higher either of these are the more critical plumbing and circulator choices become. As to storage, the higher the temperature of water you can store, the longer the times between firing the WG, unless you also need high temperature water to meet your system needs.
If this fits you, then I believe your key calculations are all about insuring that when the WG is firing, your pipes and circulator can move the WG output to system and storage so that WG idling is minimal and preferably not at all.
My earlier comments were based on delta-T = 20F; that is, the temperature difference between supply water from the WG is 20F higher than the return water. The WG likely requires 140F minimum return water, and likely has maximum output of 185-190F. At maximum 185F, and maximum return water (such as from storage) of 165F, 8 gpm's will move 80,000 btuh, which over a burn cycle probably will handle the WG E100 satisfactorily. But, if you want to bring your storage up to 175F with WG output at 185F, then you will need to move 16 gpm's to move 80,000 btuh, and if your goal would be storage at 180F, well you can see what is happening.
Don't despair. My Tarm Solo 40, rated at 140,000 btuh, has maximum output of about 190F. I can bring my 1000 gal of storage, top to bottom to 190F +/- with no Tarm idling. But you can be sure that as storage temp approaches maximum I'm no longer in high burn on the Tarm, but rather, with experience, have loaded the Tarm so that as storage temp gets less than delta-T=20F, the Tarm wood load is burning down, btu output is falling, and I don't need to move gpm's for full output any longer. Kind of like letting the car coast to a stop as it approaches a stop sign. This can be easier that it might appear, depending on your situation. That can be another discussion.
Bottom line, IMO, plan for minimum WG to storage/primary loop at 8 gpm's, higher would be better if delta-T will be less than 20F on a regular basis.
