Just as an idea, something to toss back and forth: we know George Kirk saved 800 lives. Is it possible that the Kelvin was transporting people at the time she encountered the Narada?
It's own standard crew might be a lot less than that. And if the Kelvin were carrying passengers, perhaps she had a greater than usual number of shuttles too? Perhaps larger ones with increased cargo capacity.
Why did Nero attack the Kelvin?
He'd set off on a mission to destroy federation worlds. After going through the wormhole the first thing he sees is a federation ship. He also needs to interrogate someone about the location of Spock, and isn't in the mood for a friendly chat.