Hello, everyone!
I tried search but couldn't find any answers for this situation. Can anyone help?

I have to fly MCI-ATL r/t on March 13th/14th and will drop from S to peon on March 1st.
The DL non-stop looks pretty inviting (~$170 all-in), and I wanted to book it through CO. The F cabin on both legs is empty as of today.

1) I assume that booking while still S will get me NO complimentary upgrade on March 13th. Correct?

2) The CO website seems to say that one can purchase upgrades with CO miles on DL codeshare flts. Is this true? If so, how can I do it?

3) Failing that, will a Y-up work (booked through CO while I'm still S)? If so, who confirms the upgrade, CO or DL?

I apologize in advance if these questions are too dumb or far-fetched, but I fly all my business on US these days and don't know the CO and DL systems very well.

Thanks!