By August this route should have some form of meal service return. We still don't know what exactly that's going to be yet as Delta has been awkwardly short on details which makes me think it isn't going to be a full service like it would have been two years ago. I wouldn't use this as a reason to book F over C+, especially in this situation.

I'd agree that with the lap infant, I'd probably go for a whole row of C+ just so that you don't have to sit with the child in your lap the whole time.

If you end up booking F I'd choose the 753 over the 321, if you go with C+ there's not really any noteworthy difference. The 321 C+ seats are slightly wider than the 753, but the plane is also noisier if that makes a difference to you.