The Fairies' rides are always well planned and well organised and have a reputation for very good catering! You'll love it and quickly start hankering to do a 100km...
Navigation - until GPS became commonplace, a lot of people used something like this
https://www.sjscycles.co.uk/accessoriesmaps-navigation-holders/pletscher-map-holder/ - and many still do. The more expensive plastic route holders are also very good but not worth it if you're not sure that you're going to use it more than once. At the start there are usually polythene bags for brevet cards and you can nab another to put your route sheet in, just in case of rain.
One bit of advice: a day or two before, read the route sheet and track it with your finger on a map. That way, you'll have a mental image of where you are supposed to be going, which can be surprisingly helpful if you think you may have missed a turn or something just feels "wrong". Whatever you do, don't blindly follow the person in front, even if you know they are on the same route as you. I made that mistake on my first ever Audax and spent the rest of the persuading myself that I enjoyed climbing back up Charing Hill.
Depending on work and other commitments I may pop along for one of the rides so if I see you I'll say hello.