I'm pretty sure there's a centaur body plan in the default raws.
I had put some thought into this for GURPS at one point. One thought is that the centaurs have redundant organs, 2 hearts, 4 lungs, etc, but supposedly in Dwarf Fortress they will still die if either of their hearts are damaged, which just makes them more vulnerable instead of less vulnerable as you would expect. Another theory is that centaurs are related to or descended from Nagas and Merfolk, their lower body is just a modified tail, and serves no biological purpose other than to hold up its legs. Finally, I think the DF centaur body plan treats the human torso as the UPPER_BODY, i.e. heart and lungs and the horse torso as the LOWER_BODY, i.e. the guts.
I'm pretty sure civilized centaurs will feel the need to wear shoes, even if they have hooves, but there are some DFHack mods that disable the psychological need for clothing (I think MasterWork does this). You could also give them some appropriate type of footwear like a horse shoe, but that would be civilization dependent, if a goblin bard joins the centaur civ, it'll wear horseshoes, and if a centaur joins a dwarven civ, it'll wear normal shoes. There are such things as sneakers for horses though:
The main issue with centaurs realistically is that if you just add a human torso onto a horse body we get a problem in that the total weight of the front parts ends up exceeding that of the back parts so the creature either bowls over or spends it's entire time bowling backwards in order to correct the weight balance.
I don't get that. Humans can stand upright on 2 legs, I don't see why adding a horse-behind would cause them to fall forward.