Hi shan and welcome to the grey forum. What is your new greys name ??
Do not give to many sunflower seeds as they are high in fat and not that good for them. You can offer pellets any time , but it make time before they eat them.
Your grey may be quiet for some time as he is in a new home with new people so give him some time to settle in.
You can sit by his cage and talk to him as much as you can and let him get to know you.
This should get you started.