Help me optimize this crazy giant stag beetle

I'm building a character that starts as a wildshape ranger and goes into vermin keeper

A vermin keeper gets a vermin companion as an animal companion

he can use any vermin (large or smaller) that's described in the monster manual and this vermin loses vermin traits (mindless) but gains INT 2 , the ability to gain feats and skills and it can be trained like a normal animal companion

This last part is especially interesting as it give you the option of training that thing to give it the warbeast template

Since vermin are specifically allowed to get the template, albeit in a limited fashion, the vermin keeper's special attritube of not being mindless (and trainable like any animal) should let it gain all the bonuses of the template though I could see a dungeon master preventing that.

Still, you start with a 7 HD vermin
+1 HD from the template
+8 HD from the vermin keeper progression

So by level 15 you have a 16 HD giant stag beetle

The beetle's stats are also kind of crazy

23 STR +3 (template) +4 (vermin keeper progression) +4 (from HD) for a total of 34

Beetle's bite attack deals 4d6 damage + 1 1/2 STR (18)

add improved natural attack and now you're at 6d6 +18

My ranger also has sword of the arcane order so he should have access to a lot of interesting spells and the beetle counts as an animal as far as buffs are concerned so I can even use animal growth on it

So far my plan would be to ride the beetle into battle (with a spear) and use rhino's rush to pump my own damage and the beetle's

That still leaves me with 5 feats to play with
5 levels for a prestige class (should we get there)
and access to any ranger or wizard spell to buff

So guys, any ideas?

If you are going the full mounted charge, I would recommend a lance and going down the mounted combat feat tree to spirited charge, giving you x4 damage on a charge. There are a few other multipliers that can make for a decent alpha strike, like Valorous Lance and the Boots of Riding, netting you a x6 on your first strike.

If the Beetle is charging, giving it the default Charger suite (PA, Shock Trooper, Leap Attack) would work just fine. Natural Weapon doesn't get 2xPA but it's still a decent chunk of extra damage (+24) and gets further doubled (+48 on Rhino's Rush). Some Incarnum could add some cool stuff. Totem Avatar (Shape Soulmeld + Open Lesser Chakra for 2 feats) on Shoulders gives an extra size increase for 8d6, which is nice. Animal Growth would push it into 12d6. One option, anyways.

It's from Dragonlance, but the feat Tremendous Charge lets you use your Mount's strength score when you charge with a heavy lance