He definitely gets the free sorcery/fire2 from the Blasting Workshop,the free city garrison from Gridlines, and he used to get the free heavy and light promotions when there were Armament Molds and Velox Workshops. I always wait until I have a city with both of these to build him.
Well, if I'm playing the main mod. I added retrofit spells in my modmod so that (for a little gold, a turn of immobility, and the cost of other specialized promotions) golems can get thse promotions after being built. (I also reintroduced Armamant Molds and Velox Workshop, plus a couple new UBs.) Currently (meaning in the last version of my modmod, I haven't actually updated in in a while) I have it set up so the golem casts this in a city with the appropriate building, but I wonder if it would be better to let Luchuirp adepts retrofit golems in the field?
I also make sure that I have a blasting workshop wherever I build the Mithril Golem (it already has divine and earth 3, so this also gives it the ability to cast ring of fire and crush), although since he lost his affinity I don't usually consider building it worth the cost (well, I wouldn't if I didn't mod it so he has affinity again, actually more than before).