Have to start making graphical sprites. I am notoriously bad at this, but as per the FotF response, anything that doesn't have sprites won't show up, unless I want to reuse vanilla sprites and confuse players. I'll be honest, I've been putting this off the whole time I've been doing DF modding, because I suck at it. But it's not going to be optional anymore.
I did make a golem yesterday. Theres only one variant, bronze golem with a sword and a crossbow (they have an interaction to fire bronze globs, which should be dangerous enough). I'm trying to put a special rune on them which counts as their brain, is a small, external body part made of obsidian on their upper body. It works if you hit it with an edged weapon like an iron axe, but not an iron mace. That just glances off. They're "skilled" fighters in all disciplines.
They won 21 out of 26 matches against equally skilled humans wearing iron armor and steel halberds (I figure the halberd simulates most large slashing, stabbing and smacking attacks). Those who won had one or no major injuries, the golems tended to suffer several lost body parts or serious injuries.
So they're tough. Now I just need to write up a construction/summoning reaction and interaction to produce them in-game.