Amydunn,
As said above, your best bet is to go through the NATS interview process thread - you get perspectives from people who have been going through the same process that you will for the past few years. It hasnt really changed in that time, so dont worry if they are a few years out. The thread is really useful, but it is worth remembering that it wont actually help you pass any stage if you aren't up to standard - there are no cheaters or backdoors I'm afraid!
I completely understand your worries, having been through it in the last few months - but just relax! Learn the pre-reading you got send and I would recommend maybe getting some psychometric workbooks if you a worried about the tests.
Best of luck
