I love healedabbey!
Eep, I haven't looked at it in a while.... (turns out I'm a silent stalker of most of the current "notable" forts, mwa ha ha.)
I like circles, but when it comes to building things above ground, I wind up making plain empty un lived in cylindrical/conical towers cos the part of my brain that formulates rooms when 'digging them out' is just not kicking in for some reason.
As for levels, I've got loads of trees, 2x soil and the rest igneous (gabbro mostly) and I'd like to combine "digging down" with building up, my self-imposed restrictions are at the VERY least, everything outside is made of blocks, as little cave adaption as possible (sometimes my engraver comes down with a case, when he does too much tomb-smoothing etc). I'd like to incorporate a tomb/memorial for all the dead humies, even if I can't bury them properly.
Just the river -- no aquifer or magma pipe. (I haven't managed a tree-fueled metal production cycle since my first fort) No sand sadly, but I love glass enough that I might try to hack it in (if anyone's made it possible in 40d9 yet?) As many levels up and/or down as you like! (I've got 15z underground) From what I've seen in other all-igneous layers, I should be able to produce loads of Electrum. I'm expecting iron to come in yearly goblin harvests (and I can melt the zillions of iron/steel whatevers the humans have.)
(if you care for a closer look, and the future updates, I've put the link to the dfma page in my sig)