I'm not sure if this is the right spot, I didn't see an Aeromexico forum.

I'm looking at a "mixed" itinerary on Delta.com in First Class (if you're needing to know the specifics, I'm looking at:
SJD -> MEX -> ATL -> ALB on 1/14/19)

1) Is the "Premier" equivalent to the First class on Delta? (it seems so?) I'm mostly about the wider seats and more reclining options, although some drinks and food are nice. I believe the "mixed" flight is only from SJD to MEX and then from there it's Delta metal

2) I'm confused (easily) - do I earn skymiles on the entire trip? I don't fly enough to achieve status, so I'm not really concerned about the MQM and all that.

Is there anything else I should be aware of (gotchas, or "weird things") with flying a mixed itinerary like this?

Apologies if I'm in the wrong forum.