Yes to all. Remember that skill mod max is 1, and that an animal cannot have an int higher than 2.
Yes and no. I'm playing a level 9 druid and using a Dire Eagle because there are no flying mounts that are "better" that are available as animal companions. In fact, a Dire Bat (even lower level) is arguably a better flying mount than the Dire Eagle. I'm mostly using the Dire Eagle because I love eagles. If you want your animal companion to act as a fighter alongside you, then you usually want to trade them up.Also in general is it better to trade off for a bigger better animal at every opportunity? (Yes I've seen the Fleshraker, and probably not going to use it since I don't want the DM to slap me around for using OP things :P) I do love the idea of a Leopard or Panther for my Halfling to ride though via Halfling druid lvl 1 class.