Hi watergal,
before I got Fibromyalgia I used to be an avid bicyclist. I used to ride 20 - 25 miles a day, and more on the weekends. I always participated in the organized bike rides at festivals and charity events. I never did a 100 mile century, but my longest ride was a metric century (62.5 miles). You can do it too.
First, and foremost, your bike has to fit. Sometimes even well meaning bike shop owners will sell you the wrong bicycle just to make a sale, and this is very unfortunate for the beginning cyclist. If you want to e-mail me I can figure out if you have the right size.
Next, on the clipless pedals... they are far superior to clips and straps, but there are a few "rules"
1. Always use the same foot to put down at a stop. Get used to using only that foot. Anticipate the fact that you are going to have to get out of the pedal way before you need to. These pedals usually have adjustments and can be set a little loose. Some are made to float in a side to side movement to save knees and are definitely better.
Don't be pedaling at the last minute before a light, or stop sign, and get the other foot at the top of the pedal rotation. By using the same foot all the time, you will train your body to lean to that side so you will always be balanced right.
2. Practice this skill in a parking lot. It's the same as practicing scuba skills in the pool. You want it to be second nature.
3. Make sure your seat is adjusted properly. You don't adjust your seat so you can touch the ground with your foot while sitting in the saddle. You are supposed to adjust it for when you are actually riding. I can help you with that as well.
4. Wear bike shorts no matter what you think you look like in them. They serve a purpose.
5. There are other adjustments you need to make besides the height of your seat. That is only one of the things needed to fine tune you fit.
6. Get a mirror to put on the end of the bar or brake hood in the case of a road bike. The are made for road and mountain bikes, and don't look like the old "motorcycle" type of mirrors. It is never nerdy to be safe and know what's coming up behind you. I'm assuming that you are wearing a helmet.
7. Always turn corners with the inside pedal at the top of the rotation. Don't pedal around corners, until you are coming out of the other side.
Go to the Bicycling Magazine site and read all the articles you can find, or buy the magazine. It helps to study this like any other sport.
Bicycling is a great sport, and the organized rides are wonderful places to meet people. It's like anthing else. When you know how to do it right, and you relax, you have a blast.