This is a feature suggestion or a bug report I'm not sure but I'd like that when the option "Resize interface to video size" is disabled then the ALT+1 ALT+2 and ALT+3 should still work, that way we can set the size of the window easily, I see no reason why this doesn't work right now. Also it would be nice if changing the option didn't require closing vlc and opening it again to make the shortcuts work.
Switching between these mode is a bit messy for example if I set the size to 50% and then change the option, the next time i open vlc the window size will be the last size of the window, it should be 50% but no, it's the last windows size from before the setting was changed. Sorry I can't explain this better.