As for a 3D game, the AI should be improved for all enemies. Let's face it, enemies in JJ2 are all quite dumb (only Devan can duck and he still does that badly, Sparks' tactic is way predictable), but that's mainly because that isn't all so important in a 2D sidescroller. In 3D, the aiming is more accurate and we approach the enemies by more complicated means. So, if the turtles currently just wander around and bite when we're close, in 3D they should approach the player and then try to bite him. Doggy doggs should be even more intelligent, retreating when shot and then coming again, attacking from behind by making circles around the player, maybe even jump over the lower shot bullets.

About your need for modellers - I barely can model too, but if you need a bg music, that's something I could help with. A bit.