Also, I saw a video of someone washing both (refillable) pods and coils out before switching flavours to avoid cross contamination of flavours (and as a means to extend coil life. I know coils aren’t too expensive but thoughts?
It's not a bad idea. I think people use isopropyl alcohol usually for that? I actually have five old coils that are soaking in everclear right now as an experiment to see if old coils can be reused. I've heard the wicking can be adequately cleaned with alcohol, though I'm not sure ethanol works the same, nor that coils that have sit dirty and unused for months can be resalvaged.
But yea, I don't worry about it too much when switching flavors. It depends on how much you care about the purity of your juice flavor relative to what was being used before.
Ah, and I could see isopropyl soaks before the coils go bad being an effective preventative measure, but again, I can't say from personal experience or even much research.