Hmmm, those drive team requirements seem familiar
As for the written drive test, I think the 90% seems a bit high, but that depends on when they take it. I usually give that test after a few days, so I just take all the tests and compare the results. If you're giving this later in the season, I would go with 75% or so. Drivers could still learn after the test, and you don't want to rule out your best driver because they thought a processed litter was 2pts instead of 1pt.
For choosing the driver/manipulator, I let my kids try out for both. I don't want to take a smart kid out of the drive team completely because they prefer driving over manip, and someone was slightly better at driving then them. Yes, it causes more of a headache for me (more drive team combinations), but I coach FTC where the teams are usually 10 kids. I get less kids trying out than say a 30-50 student FRC team. If this is your case, continue to let kids try out for both, but choose a driver then your manip.
Other than those two points, this is very well writen. Choosing your drivers is one of the most difficult decissions as a coach, but with this system it makes it easier. I wish you the best of luck for years to come!