I do quite a few-both as a part of organized events with others and probably even more solo. I'm finding it harder to stay with groups later in the rides so many of mine turn into a solo ride which I'm completely fine with. In fact I like it better that way as I'm riding my own pace, stopping when I want to, etc. However there is a lot to be said about the benefits of riding in a group and covering ground faster with the same effort. The key is to find others that ride close enough to your skill level where there is more pleasure than pain.
A couple of general tips on routes that might help. I find it helpful to venture into areas I'm not familiar with for motivation sake. There is some mental incentive and excitement for exploring or going to an area that makes you ride a little further than you might otherwise. Make sure your destination takes you far enough away to where you have at least 50 miles to get back to your starting point. You will find that around 75-80 miles you are going to question why you are out there. I've seen folks take shortcuts so in some sense it's planning a route that forces you to cover the full 100 miles.
I do loops, "lollipops" and Out and Backs. The only disadvantage to an Out and Back is if the wind is prevalent and strong in one direction it can make or break the ride.
See if you can plan your route so the harder part of the route is in the first half of the ride---like going out with more headwind and coming back in with more tailwind. or the tougher hills are in the first half with less in the last half. I love centuries with the last 5-10 miles are downhill.....
You really don't need as much food as you might think---you can train yourself to do with less. I've found it's just a matter of what riding habits you create for yourself. Here lately I've been making only 1 stop and that's just to get some more fluids and to just get off the saddle for 5 minutes. Yesterday I ate a small banana and 3 peanut butter crackers while I was riding.
I enjoy the centuries and the time on the bike and know you will too.
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Ride your Ride!!