I vote Yes to number 1, the cannon would be super useful. I vote no to number 2, I think the def is okay enough. When you have 2 people, one inventory will last me like 6-7 kills. I vote Yes to number 3, it would make quick banks possible and it to be easier when someone dies. As for number 4, I am neutral.
A bit more info on why I vote against number 2, if you have a cannon setup, as a solo player, I feel it would be relatively quick. Cannons hit up to what 400? And have that weird chance to proc 3 times. So having a solo with cannon feels like a duo in my head. I would want to test that at current def levels.