First, the vote is double enveloped, should you choose to do that. Not everyone does.

It gets validated, then passed along for counting.

Second, if you want, you may drop your ballot into any drop box, or hand deliver it to elections, who will validate it and put it into the counting queue.

Not so much, it shifts secrecy from flimsy booths at a polling place to the voter, who presumably fills out their ballot in the privacy of their home, and then you have the option of dropping it off directly at the county elections office dropbox instead of mailing, if you're worried.

Not necessarily. Grab a set of ballots in a public library, randomly from a pile, the way you can grab a set of tax forms.

Send them from an arbitrary public mailbox at a busy place, like a train station or a mall.

This should make tracking impractical, unless you expect "them" to scan for fingerprints.