Does the app allow to turn off/on certain expansions after purchase of the add-ons, or does it use them all the time if you bought them? I haven't seen anything yet that says one way or the other; when we play, we typically pick and choose expansions to cater to the players at hand (best to not scare the n00bs with the expansions right away, y'know?), and if this app does that too, I'll get it and all the expansions too.

P.S. It'd be nice to allow for custom characters to be used, too, but it's definitely NOT a big deal; just a suggestion for updates later on.

The app allows you to turn on and off expansions at will in the menu screen.

It has a check screen on the right. Basically you tap the expansions you currently want on and those are the ones it'll draw from. Really easy to set up.