My thoughts:

1. Exactly as Gurkhal said, although it does surprise me that Romans managed to still gather larger forces than those of Carthage's (Hasdrubal Barca's), because after all many of Roman allies have either fleed or changed side. Either the Romans too smart, Hasdrubal Barca too eager to sack Rome and can't wait any longer, or Hannibal a bit too slow...

2. That's new to me, I always thought that Carthage was going at least to march and Rome and sacked it (if not totally destroy it), or maybe if the Romans are too stubborn as you all said, the Romans burn their own city to the ground and flee to surrounding area (hills and mountains)? Just like what Russia did to Moscow during Napoleon's invasion?

3. Might as well expand from sea, Carthage are sea-faring nation after all, at least much more sea-lovers than Rome did in our history. My predict is that Sicily will of course be target of expansion, they're located exactly between city of Rome and Carthage after all.

4&5. I'll leave it later, it'll be interesting to see many viewpoints regarding these