I've gone on enough month plus long self-contained (I carried my own gear.) bicycling trips to consider myself capable of writing a book on bicycling. At one time, the bicycle was my major form of transportation.

SAFETY is the first and most important consideration. Here are some, not all, important safety rules.
1. Wear a helmut and keep it snug. A loose fitting helmet is worthless.
2. Make sure your brakes work well. Nothing on you bike matters as much. Check them before each ride. Look at the cables and the brake pads. Any bike store will tell you if your brakes are okay for riding.
3. Wear bright clothing so you will be noticed by 80 year old drivers and others talking on their cell phones. I'd suggest using a flashing night light during the day if it would not bother nearby bikers.
4. Never closely follow another biker. Stay 3-5 yards away. You never know when a person will slow down, stop, or veer left or right.
5. You need thick gloves and well-padded handle bars to avoid hand problems and for comfort.

Some important information in choosing a bicycle.
1- Safety first. Comfort second. Speed last.
2- Get a bike that can handle potholes, dirt roads, pebble roads and so on. Nothing worse than not being able to bicycle down a beautiful dirt road.
3- Bike tires should be at least 35 mm, 1.5 inches, kevlar belted.
4- Road bikes are designed for speed, not for comfort. The frames are stiff, wheel base short, and are meant to be very responsive. You want just the opposite: flexible frame, long wheel base, less responsive. You want to be comfortable.
5- Serious bicyclists ride with fenders. My bikes had fenders. Fenders not only protect you from dirt and water, but they protect your drive train (chain, derailleurs, freewheel).
6- If you buy a used bike be prepared to spend $100 to have it serviced or make sure it was serviced prior to the purchase.
7- Unless you are going on an 8 hour trip you don't need any more than 10 speeds. On bikes with 24 speeds most of the speeds are near duplicates, so effectively you may only get 10 speeds.
8- You don't need to spend a lot of money to get a great bike. Consumer reports recently tested some bicycles. A $250 bicycle was rated as a best buy. Look under 'Files' on this site for this report.