Mount Optimization

[Mongoose87]

So, my DM has given me an item that grant me leadership as a bonus feat. Groovy. However, I don't particularly feel like playing a second character, so I got his permission to use the feat to level up my Paladin's Mount. The mount is a triceratops, on the small side for its species, but about the size of a Magebred Horse. In fact, except for appearances it is a Magebred Horse.

In that respect, I have a couple questions:
1. What is the best way to maximize its speed and survivability (class-wise)?
2. Would the HD for being my mount stack with the 17 levels it will have for being my cohort, or not? Or, at least, would you expect a DM to allow them to?

[lvl 1 sharnian]

Take the Devoted Tracker feat and that will let you stack ranger and paladin levels to treat your mount as both a Special Mount and Animal Companion

[Flickerdart]

There was a Supermount build hanging around somewhere that gets it to something like 50HD, making the mount more badass than its master.

[Mongoose87]

Take the Devoted Tracker feat and that will let you stack ranger and paladin levels to treat your mount as both a Special Mount and Animal Companion

I'm not a ranger. Also, I'm using the free feat from an item to do this, all my feats are occupied.