Blimey, you make stage 2 sound a bit daunting.
FWIW I agree with you on the guessing thing. I assumed NATS are looking for consistancy and accuracy so will just be doing my best to get through as much as possible while getting them right.
I have done the little sample paper that NATS send you know, and got all of the questions right first time and well within the suggested time (1 minute for data checking, 3 mins for the other two). Hopefully that bodes well for the assessment. Would still like to do some more praccy just to make sure.