Soldier is probably the easiest. It has access to all the weapons and has a slow-mo/bullet time ability. I personally loved playing as an Engineer, though. You can summon a cute combat drone and set people on fire! Or freeze them and watch as they fall over helplessly. What's not to like?
Yeah, you should be fine. It only gets really tough on higher difficulties.
Only problem I had with the drone was the long ass recharge.
Wouldn't really call this one a supermarket, it's more of a local grocery store. They have a little Chinese hot-n-ready restaurant in there, located right next to the deli. Good food, fairly cheap, and convenient. Not the best I've ever had, but passable.