You are not new to the event, and it sure looks like you are a clever guy who actually understands thermal mass relativity. Yesterday I viewed an ATMOS gassifier with 3-1000 gallon old propane tanks for thermal mass...coated in 3" of spray foam....computer controls, blah, blah, blah. This setup is one I check in on once a winter just to remind myself of how to throw, "BURN" cash, to achieve a warm home. Sure it works, but is hand fed and labor intensive...requiring wood, grrrrrrr!
30K to make it happen..................................... and you have a triple system that offers redundancy and many options......affordable! Smart. very smart.
I believe the thermal mass storage issue is the biggest factor to consider with any heating system. Small thermal mass boilers do well at what they are designed for, however this forum's members chose a more reserved method to stay comfy that keeps the cash within our local economy. The lower thermal reserve coal boilers may be enhanced with additional storage. Axeman Anderson is absolutely amazing when you look at the size of the burn area in the chamber. Unless you have used one you can't understand something so compact can outperform things twice the physical size. The only issue with a small fire flat bed stoker is latency of the fire when power goes out. 15 minutes is the max from my observations. Underfed or AA style boilers can be a full 24hrs. Not a big deal if you have a generator, if not.....it's easy to restart then anyway.
Can't wait to hear more about you latest addition. I know you know this, but a larger thermal expansion tank might be on your shopping list. Your DHW resolution looks to be well thought out.
I always say this is a hobby where the final destination is not the goal, it's the journey that makes it fun. Lots of nice folks to exchange ideas with, and only a handful of 'A-holes' to test your sense of humor.
Don't be afraid to call Matt or Dave for tech issues. They actually do respond and will answer any question you have. My final question/comment would be why did you not go for the 220LL? The upgrade is very short money and it's like having a 454 under the tin. Two stokers if you need them, one in reserve if you don't.....I know the heat loss calc......but.......in the real world, things are different.