1. I'd say weapon hits shouldn't count, as that's the rule my site uses and we've never had any issues with it. I can see why other sites don't use it though, especially if the weapon is blocking the player (rather than hitting the barrel of an outstretched weapon.
2. I'll take any hit that strikes my gear, regardless of where it is in relation to the rest of me. I think most others do this. If I get hit in a magazine pouch that's just overhanging cover, I don't know what angle the shooter is at to say whether or not the round would have hit me if I wasn't wearing it.
3. Interesting concept to say that those with helmets have different rules that others. Perhaps a rule that wearing a helmet allows you to ignore the first round that strikes it could work. It would definitely be too difficult to marshal though, but it would give players a better reason to wear them other than the appearance (I personally stopped wearing my helmet as soon as I worked out how to cable-tie my camera to a baseball cap. Would be nice to have a justifiable reason to start wearing it again (mobility vs protection)