From what you have said I reckon you'll be fine without worrying about skinsuits and the like. Whatever bike you ride, just make sure it is comfortable. A 400 audax ridden hard is ideal prep/test. To quote an old saying, don't rush too much when you're riding, but go as fast as you can when you're stopped. If you're doing it unsupported, have all your drinks and snacks ready in a plastic crate, watch the weather forecast like a hawk and have your clothing changes planned with a few backup items in case it gets colder than you think. Know in advance what hydration you're going to use (100% electrolyte replacement can be too much and might need alternating) and keep an emergency gel or two on your person. Travel as light as you can be happy with. Some take puncture repair, others don't. You are unlikely to need more than one bottle cage. Fit new batteries to everything, if you fit new tyres, ride them for 200 miles before the event. Use long rides beforehand to find out what your palate likes in these situations, for example I would rather eat my own date/sultana flapjacks, ham & mustard sandwiches and egg custards than energy gels and I like the odd can of Coke every now and then. Get loads of rest the 3 days leading up to it and stay off the booze. Don't stand if you can sit, don't sit if you can lie down, as the old saying goes. Grease up well before you set off and try to have a number 2 before you set off. Be prepared to push yourself in those potentially depressing hours of darkness - don't let your speed drop then. If you overtake me say 'go on lad, you're a hero, you can do it'. I'll be the one on fixed with the Barrow Central Wheelers kit. Then say the same thing to yourself.
