Possibility for both mouse and keyboard would be better since i prefer using mouse. Arrow buttons should remain as it currently is to navigate menus since Body shop and Performance shop have it that way. Also i would suggest another method without modes swithcing like 1,2,3,4 you mentioned above, A bit more complicated but less button to press to do an action.
Position - WASD, W&S for Vertical value and A&D for Horizontal value
Rotate - Q/E for CW/CCW
Scale - [-] [+] , R F or anything possible
Slow/Fast - Hold Alt/Shift while pressing action button like Positioning or Scaling
Freelook - F1 to hide UI, just like on races. and WASD or numpad 2 4 6 8 to pan and pitch.
More:
Arrange Layer - Q to top [<] and E to bottom [>], same key with Rotate but won't complicate since it's on layers menu, not layer edit menu.
Clone - C
Delete - X
Layer edit menu - Z.
Position - WASD, W&S for Vertical value and A&D for Horizontal value
Rotate - Q/E for CW/CCW
Scale - [-] [+] , R F or anything possible
Slow/Fast - Hold Alt/Shift while pressing action button like Positioning or Scaling
Freelook - F1 to hide UI, just like on races. and WASD or numpad 2 4 6 8 to pan and pitch.
More:
Arrange Layer - Q to top [<] and E to bottom [>], same key with Rotate but won't complicate since it's on layers menu, not layer edit menu.
Clone - C
Delete - X
Layer edit menu - Z.