1) Try some new launchers. You can find a lot of free ones in the Play store. (I've been using Nova for quite a while now - it's the first thing that goes on a new phone.)
2) I've seen all kinds of "my phone doesn't work any more" posts from older phones "upgrading" to Kit Kat. (To me, going from working to not working is NOT an upgrade.) 4.3 is probably safe if you don't mind the locked bootloader and Knox nonsense. I prefer open source software (Android is Linux) to remain open, even if some of the source isn't.