[Zubersoft]

1) I think making the JPG match the size of your tablet will definitely reduce file size, and will make it render slightly faster. The tablet will have to scale the image no matter what though, as amount of available space for the image isn't actually the whole size of the tablet screen (there is the bar at the bottom that can't be removed with your home/back buttons). I would say scale it down as much as you can before you aren't happy with the quality. If you have no need for color, using grayscale is a great option too.

2) Managing metadata for lots of JPGs should be no different than PDF. Each song entry contains all of the metadata, not the files themselves. This is all in the database of course. I currently don't have an option to back up just the database, but I absolutely plan on adding this as soon as I can.