The new movie was a logical crap hole. I mean, it was "cool," but not cool enough to buffer the enormous ridiculousness of the plot. Getting all angry in the past and blowing up someone's planet who's only marginally involved in the future destruction of your world, instead of, you know, warning your world? Promotion from a cadet to a captain? The insanely armed "mining vessel"? Getting fired from an escape pod to conveniently land on a planet with the one person in the galaxy who could help you? Red matter?
Not that many of the old Trek continuity episodes were any better in this respect, but I'm constantly surprised by how much people liked the new movie.
Star Trek Countdown explains some of those items but you still have one or two remain.
If I recall, Nero was actually fleeing from the Romulan Empire. He was a different faction, and his only real concern was that of his family...which still was in the path of the Super Nova and still on Romulus.
As an outlaw he fell in with some rogue faction, can't recall who they were off the top of my head, who refitted his ship with Borg Technology and Borg improvements.
They had just come through the wormhole at the beginning of the Movie and were crippled by the ship to ship collision enough that they were captured by Klingons. After many years (decades even) they escaped with their repaired ship, and then had the power to basically crush the Klingons (which was the traffic they picked up on via Uhura).
He then had a little time to pick up Spock, as he figured out the correct time when the ship would appear, he did so, and dropped off Spock and proceeded to destroy Vulcan.
I would suppose he didn't expect to be taken out so quickly after his actions or he may have gone to Romulus and warned them...or considering his vendettas against Romulus as well, he may have simply done something that would save him and his wife in the future, and then proceeded to destroy Romulus as well.
Kirk basically defeated the ship that defeated Admirals and captains already...plus a fleet...it does make sense that someone who can actually do something like that would at least deserve a command. What, you want the Commander who thought up the plan of sending the fleet rigt into a trap to be destroyed promoted to Captain instead?
Plus, Kirk had already been promoted to Acting Captain by default in the film.
The coincidence of Kirk being on the same planet as Spock...okay...that was merely hollywood, nothing in ST:Countdown on that, at least from what I recall.