>Step 3 says to complete the voter's declaration. Is that where you sign and date it? Also, I'm a little confused about that part.

Yes.

In 2020 they separated ballots that arrived late, but still counted them just in case. If the race comes down to those ballots, they may resolve it in court before certifying it. If they are statistically irrelevant (they usually are) it will just be a note.