1-i was planning on doing so but i didn't have the time to do it, i'm planning on updating the game in the future so keep an eye for that, and for reference a car door/hood would be 2-3 hardness, a manhole would be around 4 and a sandbag would have a special rule that would make it have 3 hardness for purposes of defence but still have 1 hardness for every other use
2-yes, but i now realize that there aren't many remotely activated things in the game so that should be fixed in the future with me either removing the whole trap thing or adding more items to complement it
3-pretty much anything, even other models (friendly since i didn't add rules for grapping enemy units yet), and this is completly my fault as i hadn't established the terms used in the game but all of the rules apply to all units and objects, so you could for example slam an objective that needs to be destroyed against the wall to destroy it more quickly or as i said before use another unit as a shield or if you used any explosive item then it explodes hitting both units without needing an attack roll