First of all, a local grower suggests fertilizer when they probably know as much about plumeria as you do, which I assume is nothing is a mistake.
Second, adding pebbles to the bottom of a pot that has not got a drainage hole is NEVER a good idea. A Drainage hole actually removes water from the soil and gets it OUT of the pot. Your pebbles are NOT draining any water.
Plumeria are not difficult to start from a cutting, you just need patience. It does not happen overnight. Just keep it in a 6" clay pot, with drainage holes 😃👍, and you can use conventional potting soil. I use Miracle Grow because it performs well for me.
Once your cutting shows substantial growth from the top and you have several leaves and maybe a branch or two, you can just move it into an 8" clay pot. Just move the whole thing, soil and all, and then fill in with additional soil.
Give it as much natural sunlight as you can! Consider outdoors for the summer. If you can't, how about a plant light!
Now for fertilizer, just a little water soluble plant food maybe twice per year. It is my feeling that with good light, keeping it evenly moist, not too dry, not too wet, and your plumeria will perk up.
