Thanks, Gigi and Hetty! I'll let you guys know how it goes. The spot we're hoping to plant it is in a corner, but it's also on a wall with southern exposure, so I'm hopeful that it'll have enough sun.
The soil does not seem to be terribly well-draining, unfortunately, which is why I was curious if I should mix in something like perlite. Beyond the garden soil, should I put any fertilizer or other additives into the soil with my plumeria to help it along?
Finally, as far as the transplant process itself goes, I'm planning to dig my hole, lift the tree out of its pot, gently shake out the root ball, place it in the hole, cover it up, and water it. I've heard for other plants that you want to give them a good soaking after transplanting, but I'm wondering if that's right for plumeria, given how much they dislike their feet staying wet. For the root ball, should I try to loosen it up at all, or just shake it off and replant?
As you can see from that picture, we've got some bark chips spread around as a ground cover / mulch in this area. Should I replace that around the plumeria once planted, or leave it off?