On 2, I wouldn't say they are vastly better equipped, at least not in the beginning. Most of them have bolt action rifles and SMGs, which you get plenty of soon enough.
On 3, this is one of the aspects I like. These are just some crazy dudes and gals (merc tourists) who signed up for AIM, and if you want the real military dudes you got to pay for it. Maybe the weapon smuggling just cost too much for anything heavier. Live off the land type of deal. I remember watching a documentary about south african mercenaries somewhere in Africa, and just getting a small speed boat was a major pain in the ass. I think they had one AK which they shared within the group. Most of the time they just bluffed their way through stuff, but eventually they got government support and got more equipment.
On 4. I agree with this, but it has been like that since the first JA. Not sure how to balance it. But there is a cost for setting up militia, so I assume weapons are included, but then the fact remains why we can't order from that source. Don't know how to balance it.