Hi there and
to the forums!
Congratulations on your new family member! I'm glad he or she is settling in well
Although it's great that he seems to be settling in fast, it's still very important to take things slow, just as you were planning to. As Julie mentioned, he's probably submissive because he's scared, and he may regress as he settles in. Let him choose when to move on.
Keep him company as much as you can and don't take him out of the cage for at least a week so he can get used to it. If he's still comfortable with you enough to step up after that, then you can start letting him out in a budgie-safe space. Usually we recommend two weeks without getting handled, however. Read, sing, and talk to him as much as you can throughout the day to get him used to your presence. He'll start to settle in soon
Meanwhile, you've come to the best place to learn even more about the best of budgie care practices. Be sure to read through the budgie articles and "stickies" as mentioned above by Julie
If you have any questions after reading through everything, be sure to ask as we'd love to help!
We hope to see you around