lovebird behaviour concerns

I've recently (about 4 weeks ago) ended up taking in a Lovebird from a less than ideal situation. I'm not sure of their age, I know they used to have a partner who died a while back, for most of their life they haven't had more contact with people than being fed and have lived in a cage with very few old toys that only just meets minimum size requirements, and their diet was just cheapy lovebird seed mix (more recently just millet and sunflower seeds) with calcium/iodine blocks.

Bubba now gets at least two hours a day out of the cage, but four or so as much as possible, their cage is a Rainforest La Paz (with a bunch of toys), and their diet is Tidymix parakeet diet and Harrison's Pellets. Now onto the things I'm concerned about:

• Bubba has, from the start of being let out of the cage, licked walls, doors, pictures, computer screens, mirrors. Pretty much anything smooth enough to lick. I'm not too concerned about the paint doing harm since it's an eco friendly safe paint from a company called ecos paints, but I'm concerned why Bubba's doing this and if I can do anything so they don't feel they need to.
• Bubba has zero interest in fresh food, pellets, or even a large chunk of what makes up the tidymix I feed. Bread and chickweed are the only non-seed foods I've managed to convince Bubba of. Bubba does take food from my hand though, which helps (and is how I got them eating bread and chickweed) but I don't know how to make stuff more appealing.
• Aggressiveness. I feel like they're quite lonely without another lovebird for company, and they seem to refuse mine, using me merely as a convenient/interesting perch. They get aggressive (bitey) if I'm too close, if I touch something that's Bubba's, or if I stop them doing something they want to do. Any tips on forming a relationship with Bubba, or is th best thing to adopt another lovebird as a companion for Bubba?
• Bubba doesn't seem to know how to play with most toys. there are a few Bubba likes chewing/destroying, but other than that, climbing material, chewing the walls and listening to music, they don't seem to have many ways to entertain themself. They won't go on flat surfaces where they can help it, so that puts up some barriers to explorations/playing too. Bubba was overpreening to a small extent before getting destructible toys.

I don't know if anyone has any tips that might help. I know most of these things will probably come with time, since Bubba hasn't been with us long, but I was wondering if there's anything I should be doing that will help?

I would add some type of bird foraging toy, like a refillable plexiglass one you can put treats in, they are very smart little birds. My lovebirds used to like swings. I would probably focus on foraging activities in and out of the cage as well as just spending time. Maybe a snuggle hut for him to sleep in? Keep up with the destructible toys and attention, sounds like he's doing well. For adding other items to their diet, you could try all different shapes and sizes of fruits and veggies and see what he prefers. Also adding a few plain cheerios on top gets their attention.