Yes, has to be masked or glass will have glazed appearance.

I would do tracings, and make thin cardboard templates.

Put something you don't mind getting sprayed to slightly weigh them down....... think I used small pebbles.

Then follow youtube videos on how to apply spray.

60 - 70 weather is ideal.

If its that fragile you may need to cover the whole thing in Gorilla Clear tape.
Use a small foam roller to flatten it all down.

No, they don't have to be masked.

If you spray thin coat, then yes, it will appear hazed/glazed, but if you spray a very thick coat over the windows, it will cloud at first, then cure completely clear. I've done several backglasses this way.

Humidity is also important. It should be under 55%.

Done 3 or 4 never masked just poured it on

I use to cover the clear areas, but I don't spray any longer. Some use clear
mylar, but if now a glass needs attention, I apply clear vinyl that I get from
my Graphic Designer. I myself prefer it much better..

Don't spray it so closely. And/or glue the pieces down first. I made several other posts detailing the use of locite super glue with loose pieces.

Maybe. You can always knock it back with novus, and/or spray again.

It's not always going to be 100% perfect, optically speaking. It's usually fine for score displays, though.

Same. In some cases it dries and looks ok. Otherwise I just use a sharp blade and cut out the windows. Looks better than using adhesive and then you miss your mark cause you were worried about the tape getting too close which would lift the artwork.

I suppose you could spray into a small cup, but I've never attempted that.

I always thought the trimmed edge of triple thick looked terrible. Have you had better luck with that?

I’ve not done one in a while, but I’ve always masked after the first couple. I just didn’t like the glaze look. I used blue painters tape and layered over more custom clear areas that had funky shapes. Always turned out great and easy to peel off.

Watch how much you use. if you seal it with a glass look on the back. (use a lot)
and the game is in a garage and you have temperature differences the ink will pop off the glass
The back is sealed to much.

I've done it. I found that crystal clear works just as good and then it gives the ink a chance to breath (expand)
with temperature differences.

Late to the post, but I have sealed a couple of really flaking back glasses using Cling Wrap. Clay has a method on his site.

For the score reel windows I cut out a piece of cardboard a tiny bit smaller than window, that way it will cover a fine line of the opaque screen. I put double side tape on back of cardboard and stick a bolt on top. That way easy to take the cardboard ‘block’ off and holds cardboard in place.

Temp/humidity is VERY important when spraying. Need it to be a comfortable temperature without humidity or you will have a mess I also spray a pattern horizontally and vertically when covering.

I have done many bg’s w/Triple Thick without fail thankfully.