If he’d been using a hunting rifle with a basic 1-8 first focal plan optic that was zeroed at 100y, and had been using ammunition intended for hunting, one single shot to the center mass, and Trump’s aspirations for continuing to be alive would have ended.
“Well regulated” is understood to mean “trained”.
This is a settled question; 2a rights are individual rights, not hinging on whether or not I’m in a militia. They’ve been understood to be both an individual right and responsibility for nearly 250 years, despite attempts by fraudulent scholars to claim otherwise.