How to use surplus credits

Okey, I think I have the solution - for Windows Phone at least, but it might apply to Android and IOS also.

When they updated the game with the holyday stuff I noticed that I was not earning when I close the application.

But then I tombstoned the application, on Windows Phone you can "sleep" the application - it does not close, you just put it in the background. When I then pulled the application to the screen again I got the scene where you were told how much you have earned while away.

So my conclusion is that if the application is stopped/killed it will not calculate your earnings while you are not running the application. I have not tested it for Android, but if it works as with Windows Phone I guess you could tap the "home" button (hardware button) while in the application to put it to sleep. And then longpress your "home" button again to see the list of running applications and select the game.

Tested and worked on Windows Phone

It's impossible. They will never ask to go to a residential level with any spaces remaining, and the question mark behavior means you can't even be sneaky and evict someone after you see which floor they're going to.

Those characters are only there to patronize shops and unlock scenes, and it wouldn't make any sense to have a Boba Fett living in your tower and then have another one show up so you could unlock a scene with him.