For instructions about how to arrange your desktop please refer to
http://support.apple.com/kb/HT5019
and
http://support.apple.com/kb/PH13814 (most information applies to earlier OSes as well)
About the mouse responsiveness you can try uninstalling the DL drivers to exclude a possible cause. Also, since you have a wireless screen you have likely installed some third party wireless software (not made by DL).
I'd also check the CPU usage in activity monitor, other applications running, if the problem happens only with specific SW etc.
Cheers,
Carlo