The Nvidia Shield has this capability built in (use the right stick to move the cursor, and the bumpers for left and right click whenever you have a non-TV app open). Not sure about other devices.
You can use this app to use your remote as mouse.
https://play.google.com/store/apps/details?id=com.fluxii.androidtv.mousetoggle&hl=en_GB
I also recommend buy an air mouse for your arsenal.
No idea. The nvidia shield app is good enough for me.
just buy an air mouse remote, trust me, the best 10 bucks you can spend for an android tv