I booked a good deal on a one-way coach flight from PHX-EXE in March 2019 that connects through ATL. Unfortunately we only have a one hour and 4 minute connection time in ATL. We will have checked luggage. Just looking for some thoughts and opinions on the following:

1) It seems like we are at risk for missing our connection. As there is only one flight out of ATL to EZE each day, would a missed connection mean we would be delayed 24 hours?
2) I was thinking about springing for Comfort+ seating on both legs of the flight. If we miss the connection and there is no Comfort+ seating available the next day, would we get a refund for the Comfort+ upgrade?
3) I am hoping for a schedule change to my flight out of PHX that would tighten the connection even more. Then I should be able to change to an earlier flight out of PHX at no charge to ease my connection worries. If this happens and I had already paid for Comfort+ seating, would I be able to choose a Comfort+ seat on the new flight that I am switched to?

Thanks in advance. I always appreciate the insight from the experienced flyers on this forum!