"想想幾年後，自己親手帶大的孩子被領走，會不是一般的痛，還不如不開始"

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.