1. An alternative history sets people to thinking and debating. I think that it is acceptable in this case as the weapons were basically the same, but to compare any ancient captain to a modern one, would not be acceptable. The weapons employed, on the same field of battle, would dictate different tactics and perhaps, produce different results. Today, a commander would never lead his troopers in battle. His intelligence might be better. His supplies more readily available. I believe that it was Capt. Liddell-Hart who said that Alexander fought an Oriental mob, whereas, Scipio fought a veteran, disciplined, and well trained army. The comparison not only could be made to the Romans, but also to Hannibal.
As an aside, it would be interesting to compare Marshall Zukhov, and his tactics, to Alexander. And even more fiery to switch them in time, (which comparison I said would be invalid, above).
2 & 3. The precedent (if it was that) was a good one, yet his analysis, to me, is lacking in military comparisons.
4. Had Alexander come to Italy, he would have been fighting on a different terrain and against a fierce and uncompromising people. I believe that it was King Phyrrus who said something like: 'Another victory (over the Romans) like this, and I'll lose the war'.
It is my opinion, that the Romans would have defeated Alexander sooner or later.