Francesco and Shu move much slower on dirt. Also of course each character has different stats, from my experience carla is better cuz she jumps a bit higher than other characters, and shu is best of tracks with bit dirt like the tokyo or germany tracks. Mater of course is super slow (there’s an ingame achievement requiring you to win a race as him)

Most collectables are in plain sight or just behind the spawn point

To 100% this game you need to complete every mission, unlock every skill, and get all collectibles,

Wii imo, but the PlayStation versions have the ability to turn off the auto save features

Gru moves faster when he jumps, so in areas where you have to walk, keep jumping instead.