I've done a handful of 100+ mile rides on my Genesis Flyer Singer Speed, most recent was the Suffolk Sunrise (104 miles, 3.000ft climb).
My gearing is the same as yours (48:18) and I find that just about right for me - I am most comfortable at about 85-90 cadence on the flats and can cope with the short, sharp hills of up to 12% that we get around here if I take a run at them and stand and grind up them.
The only thing that really beats me is a headwind. Hills will eventually end, but a wind is constant and I find that it really tires me out. On my geared bike I can just drop it down one and grit my teeth, but there is no escape from the wind on SS. It can get to my knees if I am not careful, too much straining on a gear that is too high does mine no good at all!
Aside from that, some general long distance advice:
1. Wear suncream
2. Refuel regularly (one bar/gel/fruit + 1L drink per hour). I cut the top of the wrappers off my bars before the ride for easy access. I also graze - 1/3 of a bar every 20 mins or so and a mouthful of drink every mile to keep my tummy from cramping if I binge. I also find that too much sweet stuff gets to me after a while and I crave savoury food from the feed stations after 50-60 miles. Eat whatever your body tells you to, but don't stop too long and get cold.
3. Pace yourself. Set a realistic average time, taking into account the hills in each section of the ride. Aim to do the first third about 1mph slower than average, the second third at average and then push on (if you can) for the final third.
4. Know the hills, weather forecast and general route. Dress appropriately and gear your bike appropriately too.
5. Cycle with friends (or make some new ones on the ride) and take turns leading/resting.
6. Make use of rest stops for "calls of nature" - no fun cycling and needing a pee!
7. Have enough spares. I carry 2 tubes, half dozen patches, pump, levers, bike multitool, small penknife multitool, duct tape and cable ties, lighter, USB battery pack and cable for phone/Garmin and small first aid kit
8. Enjoy it. Take plenty of pictures, admire the scenery and be happy in the company of others :-)
J