1) I've never used that, I just use Alt+Prt Scr (screenshot of the active window, instead of the whole screen)
2) I'm not quite sure what that is. However, any graphic in-game (whether menus or text boxes) should have several number parameters including x and y values wherever they're defined. If there's more than 2, then one of them is likely to be opacity. Also, some places plainly define opacity, such as in SpriteWindow, towards the top. It may be easier though to use an image editor and modify the opacity that way.
3) I don't really know. I looked through the whole script, but playing with the numbers didn't have any difference. Messing with the frlgtextskin file (in the Windoskins folder) resulted in some strange effects, but not a smaller width (although I managed to somehow remove the stretch effect entirely). Maruno might know though.