To move my Plat installation from one computer to another . . .

For Sonar you don't need to uninstall unless your giving the old computer to someone else. 
Otherwise just leave it. you never know you might need it someday. 
Most of the 3rd party software allows installation on 2 machines. 
If your never going to use the old computer then you need to de activate using each software vendors on line installer or iLok etc. 
It's not a big deal.