Glow masks literally are just the parts of the sprite that are fullbright (or sometimes additive blended) on top of the regular sprite. You simply copy the original sprite and edit out all the pixel colors that wouldn't glow. I tend to make the darkest of the glow parts semi-transparent as well.
Terraria supports Xinput. If your gamepad supports Xinput, it should work. If you have an old DirectInput gamepad, you may need special third party software to 'convert it' to Xinput. I don't have any official information for you on how to go about that, however.
I used to use xpadder many years ago, back when it was a free and safe standalone utility... but then they turned into some shady paid app and I went to joy2key. A shame. Didn't think anyone would still be using xpadder tbh! Good news is you won't need it after this update! :)