Austin's slide was not legit and could have been called. The "new" slide rule requires that the player be able to and attempt to remain on the base at the completion of the slide and also not change his path for the purpose of initiating contact with a fielder. I went back and watched the replay in slow motion: Austin overslides the bag - not by a lot, but he does, and while he probably could have reached back to grab it, he didn't attempt to do so, probably because he knew he was already out. But that's a violation of the rule, as currently formulated. He also alters his slide to make contact with Holt. Did he "change his path?" Less clear, but he never even tries to contact the bag with his lead foot. He sticks it out and to his left - a solid foot inside the bag - directly at and into Holt's leg. The ump could have fairly called him out on the slide for either reason. But in any case, Holt had a legit beef, and I would have expected Austin to get a suspension for triggering the whole mess even if he hadn't charged the mound (although it would have likely been fewer than 5 games in that case).
As for the suspensions, they're about right, imo. I think Kelly got the extra game for throwing at the guy twice.