Hi Folkeye - I think I'd like to weigh in on this. Earlier this year I got a male parrotlet that was a heavy plucker. He had no feathers on his back, no tail feathers at all, or wing feathers. It just broke my heart. But now, he's fully feathered and beautiful and I'm working on getting him to fly. What I did is I used the plucking behavior to my advantage - meaning, I gave him seed covered pinecones (he liked them), the Wesco kabobs (love them), I gave him paper boxes with treats in them, and corn on the cob, leaving the corn ON the cob. I also feed him a lot of vegetables and soaked seeds and sprouted seeds - he loves them, as well as scrambled eggs. Other thing I gave him is I hung a millet spray holder from the top center (so he had to work to get at it) and filled it with organic millet, nutri-berries and avi-cakes. The common theme here is it is a bunch of stuff that he had to pick at and work at. I did also get a female parrotlet that had been a lone bird, like he was. They bonded very quickly. If I was you I'd move your parakeet cage next to his, so that they are in close proximity but not close enough to beak each other. The diet you are giving your bird is excellent, but I would add some scrambled egg (about twice a week) and definitely do try out soaking seed and sprouting seed - try Higgins soak & sprout, or Higgins Sunburst soak & sprout - my birds LOVE it, racing to the food dishes when I give it to them, and it's soooo simple and easy to do, even just soaking the seed mixture in water overnight is good as the seeds plump up and gain many nutrients; and in a couple days they sprout and if it goes well you can get yourself a seed sprouter - very cheap on Amazon. I know I'm being very detailed here but this is an issue I'm passionate about because self-mutilation and plucking just tears at my heart. If these things fail then I would collar him, or jacket him. One thing I find very interesting is that birds in the wild never pluck, only birds in captivity. A plucking bird in the wild would not survive very long. Anyways... try some or all of these things, search Amazon for the Wesco Kabob, and Higgins soak & sprout - all are easy to find if you just look. I think your bird is just so beautiful - he is exactly what I wanted - I love that blue. Mine are both wild-type green, but I love them dearly. If you do get him a female you will 'lose' him to her, but that might be just what he needs - I found it to be a good trade-off (the female HATES me lol). But the fact is that 2 parrotlets is not much more trouble than one, although they are pigs when they eat for such little birds, they definitely eat more than my larger lovebirds, I often call them piglets rather than parrotlets
Good luck.