If you made dinosaurs, I would love you forever and then some.
With the wimpy default mobs, I have free roam at night, but with dinosaurs, I may never feel safe again.
With dinos, i think the spawn and despawn range should be high, as in you wouldnt be able to see them spawn or despawn and the same ones spawned would stay spawned while your within [some large] radius of them
A suggestion... SLLLLLOOOOOOOWWWW down the tortoise's walking speed. This will make them both hilarious to watch, easier to keep track of if they're carrying your stuff, and well... more tortoisey. I was half expecting the big long opening minecart ride to be rudely interrupted by a tortoise slowly and painfully crossing the tracks.