The militia clause should not matter. A militia is not the same as a standing army. Militias are called in the absence of a standing army, or to bolster that army's strength. The whole idea of a militia is that it consists of citizens bringing their own weapons to the fray. If the citizens were not allowed to keep and bear arms, they would never have the opportunity to form a militia.
Not necessarily. If a citizen had a weapon, it was more than likely an expensive rifle, suitably accurate for hunting.
The Militia used inexpensive, smooth-bore muskets, and the militia member had 6 months to acquire one. Muskets were quick to reload and more suitable for the rapid, volley fire used in battle.
It’s the segment of the phrase “well-regualted” that gives the other side the ability to litigate on the basis that means the National Guard, as 5000 guys just showing up with their guns would not be “well-regualted.”