I can see the 5 characters, 5 vehicles reasoning but it really depends on how it's going to be implemented. There's still a few factors here although I could be wrong, I've only skimmed the past few pages. If the characters are digital, then they can be switched about easy enough between the different vehicles. Another factor would be how many characters are up front. If the rumours are true about the guide/driver getting attacked, then we're going to need somebody else to take over driving, which would suggest at least 2 people up front.