Seems simple enough. Along with the arrows, the “X” and the Check, a button that prevents further manipulation of said fixture until it’s click again.
Seems like it could be a good idea, especially to avoid moving vents when making LED lights. With all these possible additional fixture buttons, the screen would be completely full with different buttons to change a fixture… 
I think a better way is to keep a fixture selected for scaling, moving etc, until you click the green “V” button. The next thing you select then will be the next fixture to move untill the V is pressed.
This could be easier than implementing a layermethod for the fixtures.
Sounds quite workable to me! A keyboard shortcut to select and maybe a tab function if multiple fixtures are in a single location? It’s so annoying working with grilles and vents, as they seem to always be “on top”!!!