If you find that you need a new saddle, they are pretty much universal. If the saddle that is on the bike works for you, don't worry about changing it. The first several times that you ride, the saddle is going to be uncomfortable and you will have some slight posterior pain after getting off the bike, even if this is the perfect saddle for you. It takes three or four rides to break your backside in. If the saddle is not a good saddle for you, there are several ways that you will find out. You may feel numbness in which case you do not want to ride with that saddle anymore, at least not if you want to give your 8 year old any siblings and keep your wife or gf happy. You may feel intense butt pain during the ride, or you may still feel pain after riding your bike for a month or more. If any of these things happen, then you will need to change saddles. If this happens, you are going to wish that you lived closer to a real bike shop. Most bike shops have some sort of policy where they will allow you to try a saddle out for a week or two, and if it does not work for you, you can return it and try a different saddle, and so on until you find one that does work for you.
At this time, don't ride in the dark if you don't have to.
Bicycle traffic laws vary from state to state and city to city. You need to use your computer and look up the laws in your state as they apply to bicycles. For the most part, if it is legal for your car, then it is legal for your bike. If it is illegal for your car, then it is illegal for your bike. As AlanG said, a bike path or dedicated bike lanes are the best places to ride until you are more comfortable about controlling your bike. Low traffic country roads are OK too. Just make sure that you are wearing highly visible clothing so that the motorists can see you.
Don't think carb loading right now. It will not work until you are in a training program. You need to increase the amount of glycogen that your body can store before you carb load, and that is done through the kind of higher intensity exercise that you would get when training. If you try to carb load now, your body will store it all as fat. All that you need do at this point is just eat normally. I would eat a little higher carb breakfast than normal, something like pancakes or cereal with fresh fruit. Take some snacks along. The amount would depend upon the ride. I like bananas because they are a good source of carbs and potassium, and the wrapper is biodegradeable. It doesn't hurt anything if you throw it in the bushes. Any kind of fruit is good. You can buy energy bars in most grocery stores now. Sporting good stores usually have things like gels and other energy preparations but they tend to get expensive. You can always fill your water bottle with Gatorade for short rides.
Shortly after your ride, within an hour or two, you want to to get some protien to aid in muscle recovery and some carbs to replenish some of the ones that you used. A cheese burger and fries would be great except for the fat. My choice for a recovery meal is a Subway roast beef sub with all the veggies.
There are no foods that you should avoid that I know of. Just eat like you did when you were running. No huge meals before you get on the bike, no turkey because of the tryptophan which makes most people drowsey. It goes without saying that you should not get drunk or high before riding.
By the way, when I mention rides, I'm not talking about a spin around the block. You don't need to rush out to Subway because you rode down to the end of the driveway and back. Short rides are usually like 15 miles or less and you really don't need to do anything special nutritionally for that.
