First off, I do not think that you have the Celadine (notice spelling). Your branching, leaf-shape and size, and recurved petals are not Celadine-like at all. I have included photos of the flowers of several of my Celadine. You certainly should not use fertilizer while your cutting is rooting. Without roots, well, there is no nutritional intake. Misting probably won't hurt, but also probably won't help with rooting. You are rooting it about what I do with mine, but I do keep my potting mix damp. I used to worry about rot if my cuttings got wet, but no longer do. A well-callused stem doesn't tend to rot when you are rooting it.
All this being said, your cutting may be rooted. Have you gently tugged on the plant to see if it comes out of the media readily or resists lifting?
What to do while you are gone? Humm, that's a tough question. If the cutting has rooted, you need to have someone water it while you are gone. A potted plumeria that is well-rooted uses water at a pretty rapid rate. If it isn't rooted, you won't have to worry about it. You've kept it dry for 3 wk., so another couple of weeks won't matter a bit.
How much direct sun will your plumeria get,
@FlowerPOWER, spring and summer? Plumeria are tropical trees, sun-loving trees, and in my experience, growing many hundreds of plumeria over a 25 yr. period, you will neither get good growth nor flowering without at least 6-8 hr. of direct sun. Your LED won't nearly make up for lack of sun. What do you plan on doing with it when it gets cold up there (and cold comes early for you)?
Welcome to NGA.
