Chimney / Fireplace Construction Resources

What materials (books) / website / professionals (mason, architect) should I consult about how our chimney / fireplace is constructed?
Should an office of my county have residential building plans?

Purchased a 1970s house that has a chimney with dual 12x12 flues, one serving the main floor double sided fireplace, and the other the basement single sided fireplace. It sits in the center of the house, and in the basement I can see that the main joists are supported by it (somewhere as there is drywall ceiling obstructing the view). In the attic you can see that the structure is mostly concrete block, but outside (above the roof) and on the main floor and in the basement it is veneered with red brick.

The basement has a cove for storing firewood, and when I stick my head in and look up, I see concrete block that are partially resting on metal beams that run lengthwise the stack. The hearths on both sides of the main floor measure out to be floating above the basement, so I assume there are metal beams running width wise to support them. Previous owners had a hole cut into the side of the basement stack into the basement flue to vent some furnace. Based on the appearance of the crown and where the flues terminate, it seems to me that the stack arrangement was designed for a third, probably smaller, flue tile. I would like to know how a fireplace / chimney is constructed so that I can better consider my options:

Could the hearths be removed, and the firebox floor be brought down to floor level and purchase a stove instead of an insert?
Can the basement hole in the side be increased in size from its current 5" diameter to support the vent diameter of a coal furnace?
If there is an un-utilized flue space, and I were replace the crown and open it up, could be used to for radon reduction piping run... or high efficiency gas furnace vent... (both PVC)

Seek a seasoned mason by the reference of your local masonry/concrete/block supply dealer.