Hi Darkmocha & Welcome.
There is a ton of information in the bird food room on diet.As Siobhan im in the UK & all of the seed mix's i know of contain nuts.Perhaps some of our US members will be able to advise you.
As for introducing a cage,perhaps have one set up all ready for your grey for when you bring him home,have his travel cage set up near the cage & hopefully over time he will be able to make the move.
Is he handable ? As you know time & patience is the biggest factor,im sure given time you will reap the rewards from him.
Look forward to hearing more from you