I doubt they'll use bombs; it will be incendiaries. The "environmentalist" left has assured that many cities are surrounded with "green belts" of combustible vegetation with which to get that city burning. Firefighters are not equipped to stop such fires, as bringing in a bulldozer to flatten whole neighborhoods to stop the fire would not go over well as a plan.
1) If you mean make like a California fire? Only if it is tightly compact residential intermingled with forested area. 2) If you are talking about setting farmland on fire to get to large, downtown areas would be a wild pipe dream. While farmlands do have fires, lots of farmers are well aware of that could happen and do have protections for it. Assuming they all get enough effort to start something major, it would eventually end in the suburb area near major downtown cities. All this while places still have better management of these things than California so they are pretty delusional if they are going to get the same or worse affect in other states, even with organized effort