It depends how big your hand is
The softball glove was invented in the 1920's.
A baseball outfielder glove is usually 12 1/2 to 12 3/4 inches from the tip of the index finger to the heel of the glove. A softball outfielder glove is usually 13 1/2 to 14 inches from the tip of the index finger to the heel of the glove. Since a softball is larger than a baseball, a softball glove will be larger than a baseball glove. However, this doesn't mean that you can't use a baseball glove for playing softball. It just means that you will have less margin of error when catching the softball because of the smaller pocket a baseball glove has.
No, the glove is intended for baseball, by fielders and pitchers who want a little longer glove for scooping up balls. It can be used for softball, bit does not have a larger pocket that would make a strictly softball glove better.
The binding of a glove is typically used around the outer wrist and palm area. It's used to looks and to soften rough areas. Check out Akadema's glove builder and it will outline where the binding is.
Sure. A softball glove is made of the same materials that a baseball glove is made of (high grade leather). They need time to be broken in. Oiling the glove will help with this process.
no shorter than 12, no longer than 13
It is hard to purchase something like a baseball glove online, you don't know how it feels. I suggest you shop around at the local sporting goods stores and find the one you really like, it is appropriate for your position, age, and price range. Then go back and find the same glove online. The main goal being getting a better price, just remember to add shipping onto whatever price there is, so a site with free shipping and a lower price would be the best. Every glove manufacturer makes a wide range of glove options, I recommend not spending a bundle until you have advanced to a point where you intend to take your sport into the high school and collegiate level, or if you are in a traveling competitive league. If you are going to drop 2-300 on a glove you should be done with most growth spurts and be prepared to keep it in good shape for several seasons, gloves need to be oiled, and restitched when needed, if you do this a really good glove will last you many years.