Any orthogonal connection will support... north, south, east, west, up or down... but NOT diagonally.
You could have the whole thing hanging down from a single support, if you wanted to.
I'm planning to use a giant hammer as a defense against sieges... "The Hammer of Armok", with its single support released by pulling a lever. Directly underneath it will be an inlaid mosiac spelling out "Stand Here".
I would fill it with Magma if there was any on my map... there isn't, so I'm filling it with Rhesus Macaques.
That's perfect then, Thanks. Also, I think I have a new quote

The only problem I foresee, unless you build and then remove the layer(s) that would have connected the base to the ground, is actually constructing it.
You could send out bridges from a (temporary) scaffold to build a set of walls and access floors at an arbitrary Z-level, then build walls at the Z-1 from the bridge, and so on down to Z-n, 'm' levels above the ground, but it'd probably be easier to build from the ground, with endo-/exo-skeletal access infrastructure, linking to the edge support at your upper connection point, then 'retreat' down, removing whatever you don't want to remain, including the entire [edited-in-'cos-I-prematurely posted: "...unwanted ground-to-intended-posterior support structure".]
(Unless, and I might be wrong in thinking you can't, you can construct an up or up/down stairs on Z-1 while standing on some down-accessing other stairs on Z=0. You can /dig/ them, but I don't think you can construct, the same way as you can construct a Z+1 down or up/down stairway from an up-accessing one. Also possibly at issue, removing, the Z-1 stairwell items from the Z.)
I think I'm okay for construction, I'm putting a sprial staircase up the centre of the shaft as part of the design which is allowing me to build the tower portion without outside supports, once I get to the hammer heads I can build rows of flooring out from the tower and work them from the inside out, then just remove the old connecting walls where the bottom of the heads flare out from the shaft.