Off to the right, there's a "Choose" button. Press that and navigate to where the Topaz app is on your Mac. Choose it. Don't choose the installer.
After you've chosen it, click on the Preset dropdown again and then click on the Update Preset line in the menu:
Sure. There's a Keyword List on the right side of the Library Module. If you don't see it there, type Ctrl-3.
You can right-click on a keyword entry there and choose "Delete" from the context menu that will come up.
The EV value is within a gnats eyelash of -1/2. Double the numerator differs from the denominator by 1 in the last place.
My guess is that LR's routine that converts floating point values to fractions is messing up a little. Do all your fractional EV values show up looking that funny? What...