"想想几年后，自己亲手带大的孩子被领走，会不是一般的痛，还不如不开始"

Then hire a lawyer and do it right.

You didn't even say which state you are adopting, impossible to answer.

Ultimately, the court look at the "best interest of the child" when dispute arises. So if you had a good family life and the child was happy, it would be difficult for the birth mother to take the child back.