Miss poppy

Hi everyone, around a month ago, Mr Grey came into our lives, he is a young adult male CAG, we are not sure about all of his history but the last six months had been very stressful for him and he was completely bald when he came. He was only supposed to stay the night, but he decided that he really liked my partner and I and that he was staying! We quickly fell in love as well. I have been doing lots of research and have tried to provide him with the best possible environment and diet, I don't think he was given much fruit and veg before we had him, and has never had a complete pellet, so we are finding this challenging but are not giving up! He is loose around the house all day and evening, only returning to his cage to sleep, he flies around after us following us from room to room, and loves a head scratch in the evenings. I am concerned as he does not play with any toys or items and doesn't chew either, I have tried showing him by playing myself, but he's just not interested. I have also tried hiding food and making things for him to forage, but again he shows no interest. I am worried that he might not be stimulated enough? He had not plucked at all since we had him and was looking amazing, until yesterday when he started plucking again, he has had a thorough health check by an avian vet, he is showing some sexual behaviour towards us lowering and crouching his wings and has tried to mate with our hands, is it possible that the plucking is sexual frustration? What can we do? We don't encourage it we just put him down but still talk to him and offer him an almond or something to take his mind off it. I really want the best for this beautiful bird, do you think that he would prefer an aviary to spend time in, or the company of another bird? Apart from this he appears to be very content. He chats away to us all day, and likes to sit on our shoulders as we go about our business watching what's going on! Sorry for the long winded post and thanks in advance for any advice and help!!