Hi,
Sticky on back means they are gummed or have gum, which in stamp collecting is called mint. (as good as new from the post office) Lots of abbreviations like in any specialized are.
If you hinge a stamp or attach a hinge to a stamp then that does decrease the value of it but in stamp collecting everyone does their own thing so some do hinge their stamps, used or mint, just so they can display them or put them in stamp albums or on pages.
The pin holes are known as perforated initials or inscriptions or Perfins for short. Some people collect them.
Stamps are like anything else in that the condition of a stamp affects it's value. A stamp like new is worth more. A stamp with gum missing from the back, paper missing from the front, having rips or tears or thin spots in the paper or color fading or stains or creases or missing perfs (the wiggly bits around the edges) can change a stamp from a good one to one that hardly anybody wants.
Mainly because of a stamps rarity. Because most stamps are not rare. Those that are hard to come by will still have value even if they are damaged as some cannot afford or aquire a good copy so a so-so copy will do.
Subway is a known and respected online stamp supplies supplier. There are others and you can look around and then ask here or search here and read a bit and others have mentioned suppliers on here before.
ebay or BidStart or DelCampe or Wensy and online auction sites with stamps and supplies too usually. There are others also.
Depends on what you want to spend.
I know that with me, the stamps I want to keep and protect, I use the 3-ring (for a binder) Vario plastic pages. I also have some stock books with strips in which the place the stamps. I used to have albums on paper pages which need either hinges or plastic mounts (better for mint stamps) to attach the stamps to them.
You can start cheap and once you get an idea of what you might want or need or see how other people do it then expand or change how you do things.
I do tend to go on don't I?

