Yes it’s quite simple to do this kind of layout in Makie, you should have no whitespace issues and can place the legend wherever you like.
For starters, have a look at legends here http://makie.juliaplots.org/stable/makielayout/legend.html and at general layouting here http://makie.juliaplots.org/stable/makielayout/tutorial.html
I don’t have time right now to do an example but your request should be easily manageable with those references.