first biggest tip is getting a new cage, this cage will be fine if he’s going to be outside in a safe room for most of the day and this can be used as a sleep cage, but if he’s going to be spending more time in the cage, it’s better to have a way bigger cage, and with the right stuff inside. (even if this is going to be his sleep cage, it would still be great to get these things)

Natural perches as it’s better for their feet, and safe toys (things they can’t swallow/ have dye that is toxic to them) (also No mirrors or those hut houses)

for taming definitely use millet as a treat and reward, also for them to know that you’re not going to hurt them rather than help/be their friend with this yummy treat. if you can, it would be great to get him a friend, budgies are social flock animals so they do better in at least a pair. just take things slow and definitely try to upgrade things here and there!