The roads around here are soaking and full of debris. It doesn’t seem to get any better this year. I don’t usually like riding with mudguards, but it seems better than having a wet bum all the time.
I realize I’m a little late to the party but for 200K audax / randonnée any bike should work. You have ample time to complete the event and shouldn’t have to worry too much.
I’ve done it on a steel race bike from late 90s, aluminum bike from the 2000 and carbon bike “endurance” bike from 2016. As well as on a dual speed Brompton and a cargo bike with 1x10.