The wing acts as both a brake to slow down and as a stabilization device. Skiing with a wing on your fin will make your ski feel more stuck to the water than skiing without it. For this reason you really don't typically need a wing until you are at your maximum speed and a shorter line (less than 15 off).

Adding wing angle will hold your ski deeper in the water, resulting in increased deceleration.

Reducing wing will loosen your ski up, make it ride higher in the water and carry more speed longer before decelerating.

Blade placement (up or down) is the reason for putting the wing "up"or "upside down". Typically blade-down is "upside down" but in the last couple years, manufacturers have been putting the wing screws on the opposite side, so in fact upside down is now right side up.  We'll stick with "blade down".

The blade being placed too close to the bottom of the ski will result in cavitation between the blade and the ski. This will defeat the purpose of the wing in some cases, actually making the ski less stable.

The size of the wing will also magnify these effects. A small wing can be placed closer to the bottom of the ski (possibly blade side up) -- but this will still feel less stable than a big wing blade side down. The small wing blade side up will still be a faster set up though, even if it's positioned with more angle than the big wing blade side down.

Regular size wings should typically be placed blade side down for best effects.

I haven't done any experiments with placing the wing forward or back. I imagine it would effect the ski more if it were placed at the back of the fin.