Legal Question in Family Law in Texas

That will depend on what the waiver of service says. If he waived his right to notice of a final trial and entry of the order, then yes. If not, then he needs to be served with anything that you intend to do.

Maybe, it depends on what the waiver says. If the waives the "right" things, then he does not need to sign anything else. If on the other hand, the waiver is vague or does not say the right things, then the judge will probably require a signature on the decree.