Cool! Pretty easy answers.
1. Barter works like a stat now, measuring your ongoing economic position, which is like a combination of flow-of-resources through you versus your social footprint in the surrounding society. It doesn't go up and down as you spend and gain like cash. Instead, it tells you how much of a hassle it is for you to buy things every time.
I think you can just change your scavenge choice when you want to during play, whenever it makes sense for you to be able to.
2. Sniping is definitely officially doing battle, not anything else. If your target's not in a position to return fire, then in the exchange of harm, they inflict 0-harm, that's all.
3. Living expenses are gone too!
In general, Burned Over isn't about scarcity the way Apocalypse World is.
Thanks for asking!
-Vincent