I'd recommend Speer 135gr Short-Barrel Gold Dot +P if you're OK with the recoil and Federal 125gr Nyclads for a lower recoil alternative.
However, the best self-defense round is the one you shoot best in that gun. If you get the gun, I'd suggest getting a box of each type of ammo you're interested in and shooting them to see what works best for you in terms of reliability, muzzle flash/blast, felt recoil, controllability, and practical accuracy. The one you shoot best should be the one you choose. If you shoot some or all of them equally well, pick the one you can get the easiest, whether that's in terms of cost or availability. The best wonder round won't do you any good if you can't hit your target with it.
As for the gun itself, as long as it's in good mechanical shape and you're satisfied with how it fits you I say go for it. I would suggest bringing a good light and magnifying glass and checking for cracks in the frame under the barrel/forcing cone area. This can happen in some airweight J-frames, usually from the barrel being overtorqued during installation at the factory.
