Oh, I have ever admired your playstyle, but this seems like you have some dirty tricks hidden in your sleeve!
I must say that the idea makes me a bit crazy. Maybe, for realism, if we make them bright colored with some rope down to look like air baloons... ( no, it is even worse ). I have to ask: what is your render distance? My maximum is under 500 blocks, so aren't these floating islands (that I suppose must be visible from bigger distance) a bit overkill in case of average render distance?
I got good experience to mark two of my important locations by placing a gallow to a most prominent hill nearby (so it is visible from 200-300 blocks around, enough in my case), and make one wing to point to the exact location in the walley, where second marker is placed. And to defend my aesthetics feel, yeah, gallow is not aesthetic at all, but I promise to experiment with nicer markers made from 6-12 blocks in the future!
However, the night trick with firepits seems cool, it is definetly worth to try.