Hi John Leisure line makes a small 'baby boiler' that comes with a backup oil gun so you can use oil if you are going away for awhile and could not use coal in the boiler. You may be able to do the same with your existing oil systems.
My boiler building was an old, existing stone outbuilding with a collapse roof, I resurected it by putting a new roof on it many years ago, but then decided to use it as a remote boiler building. This building is roughly 13'x20'.
For me, with the large amount of coal burnt and large amount of coal ash generated, I didn't want the boiler in the basement, the logistics of getting coal into a basement, even with a coal chute and coal bin, were daunting, and then the hauling of coal ash bins up basement stairs was more daunting..
AND couple the above thoughts with the desire to also heat by coal, my large workshop which is 280' from the house. The location of the exixting building with a restored roof that was 1/2 way between the two buiildings, well it worked out pretty good.
Also when i installed the coal stoker, the house only had a rudamentary 'cellar' with limited ceiling height, and poor stairs for access.
But since my "HUGE Project' house partial demo and rebuild, I have a wonderful basement and would consider a small LL110 boiler in the basement and a similar one on the shop,,, maybe.. It would still not be as nice logisticly, to keep the work and coal and ashes outside.
I had radiant hot water floor heat in the new section of the house, and in the entire floor of the work shop [40'x60']
To be Blunt and an evagelistic, and probably even a Zelot... I WOULD NEVER BUILD A HOUSE WITHOUT RADIANT FLOOR HEAT IN OUR CLIMATE
The comfort is just hard to describe,, it does cost a bit more than conventional forced hot air [aka Scorched Air] or hot water baseboard, but like I screamed above, I'd never do without it again by choise.
As for other boilers and logistics, there are two stoker boilers that I like and recommend that have an almost unlimited size coal hopper, those are
the Axeman Anderson boilers, 130btu and 260btu, and the EFM boilers. Both of these boilers could have a whole winter season sized coal hopper built into the coal building as part of your built to design coal boiler building.
There are many other boilers that will go 2-4 days on a load, and these other stoker boilers come in various BTU outputs, configureations etc. [ I see MORE reading in your future !!
OK, my fingers need a rest.