I know how disheartening it can be when you get a grey with high hopes and you are met with a cold shoulder. A grey is very intelligent and they build strong bonds. It is like taking a toddler from all they have ever known and expecting them not to throw some sort of tantrum. It is going to come in one form or another.
I rehomed a grey of 30 years this year. It is very slow progress, but if you are in it for the long haul, it will be worth it with every baby step. Just have patience.
If you notice he is territorial of the cage, move him to a perch elsewhere or another room while you clean and situate everything in it. It also helps to train in a room away from the cage so they are more dependent and are encouraged to trust more. My grey will not step up from his cage, but if he falls or flies somewhere, he already has a foot up waiting for me to save him when I arrive there. A little push may often helps .
Since my grey will not step up from the cage and he comes out as well, I have discovered if I put his favourite treat in his bowl or just inside his cage, and step back, he will go in. Not every day but for the most part. In the three months I have had him, he has only slept on top of his cage thrice.
Another thing I have remarked is if he comes out any later than 6 pm, he resists going in. When it begins getting later and he goes in for a drink or dinner, I close his cage. They want to roost on top of their cages in the evening so they are at the best vantage point (feels safe) at night. It is easier to avoid the situation than to pressure a tired, cranky bird into his cage.
When he bites, try not to make a large deal of it (even if it hurts). They now and then do it for the reaction whether that is a yell, a mean tone of voice, watching you jump, or to make you leave them solo. We can usually watch their bodies and eyes closely to anticipate a bite. I have yet to be bitten (though I am sure it will come). I often go at his pace and I repeat regularly any routine or progress so he knows what I expect. They are very clever, and half the battle is not letting them outsmart you.