We flew the AA 10am flight to JFK in last May and stayed at the Sheraton MXP the night before. It would be our 5th or 6rh time stay there. Whenever departing from MXP in the morning, the Sheraton next to the terminal cannot be beat - use the side door that opens to the terminal inside, not the front door.

FWIW, the club lounge during our May visit has had some improvement from our last visit 2 years ago.

We did not do OCLI - not even sure for flights returning to US can be OLCI.

We found out the walk to the US airlines check in area is very long - it is in a separate area from the main hall, and it even has its own xray machine but not required everyone to use it in order to arrive the check in counter (the area is separated into 2 compartments, with full wall separation - IIRC AA & UA on one side, DL and EY on the other side).
We saw a young couple with backpacks were asked to put their backpacks thru the xray machine but the guys there did not bother with our rollers.
After checked in you would walk back out to go thru the real security check to the gate. AA uses one of the nicer 3rd party lounges at MXP, it also happens to be a PP lounge.