Thank you both for the helpful and prompt responses! For #1, I'll do as you both suggested and omit image entirely (leaving the background black) and let the user choose the transition for the video, assuming it will fall back to images if no videos are found.
For #2, That solution seems to cause other issues...either BigBox fires an exception saying "ItemTemplate" cannot be used more than once, or once you select a game, the game title shows at the top but all the text in the list below (play now, rate the game, etc.) is missing.
OK what's the more robust option to resize the font in a listbox with a plugin then?