A note for the Philosopher Stone effect is that Homonculi in D&D are basically a Familiar with an ego. Nothing like the FMA version. You'd have to generalize to all Constructs, probably with something like 2 charges and 1,000 GP, +1 charge and 5,000 GP per CR of the Construct. Then you can introduce some new Constructs to capture the feel of the FMA Homunculi, without the baggage of the existing version's absolute difference.