Combat armour and laser rifles would be sufficient to hold off raiders and such - see how the Salvatores became the dominant gang in New Reno simply on account of the Enclave supplying them a reliable supply of laser pistols.
I might shy away from being too ready to give people energy weapons in large amounts, but yeah, that'd be the general idea. Give your militias enough to make them superior to other wastelanders, but not so much that they can't be easily taken down be well equipped Enclave soldiers if they get funny ideas about where they stand. It would depend on the threats present in the area. If the threats are tribals or people with pointy sticks and rusted out single shot weapons, then a flak jacket and an assault rifle makes the militia into gods. If the raiders are well equipped and organized, maybe revisit that laser rifle idea. If that won't cut it, then the Enclave proper will need to pacify the region.
Speaking of gangs and raideds, would the Enclave try banning or regulating chem use as well as people having access to firearms? Some people can get their hands on a mininuke
I would say yes. They dealt in chem trades in FO2, but that was with people they intended to kill, anyways. Part of remaking civilization is instituting law and order, and you can't have rampant chem use and trade destabilizing all that.
Guns are a little fuzzier, since you have to have people protect themselves, and as stated, they Enclave can't be everywhere. Having militias means access to arms. I don't expect a full 2nd Amendment style rule though. My impression is that the US government had slipped into full authoritarian some time before the war, so I don't expect the Enclave holds to the principle of a right to bear arms.