A: How would one choose who is in the Militia? Personally while "everyone is in the Militia" is a nice sentiment. I know of far too many people who cannot be trusted with a dull flimsy plastic spoon.
How picky you can be depends on how many militia you need, what you need them to do, and how soon you need them to do it.
Also,how many things do you need them to do? You can include people in the militia and not have them in combat positions - communications, support supply, labor, etc.
B: How would one equip said Militia and with what? While Peru had the Ronda Campesina they armed them with shotguns. While this did work to a degree it was found that the Sendro Luminoso had better ranged weapons and could pin down local militias.
How much funding is available, and where in the world is this? AK-47s in some version are available in across most of the globe, as is its ammo. It has the advantage of accepting a lot of abuse and minimal care. And it fulfill your range requirement.
Uncle Ted