United Airlines at SFO

I am flying from Australia To San Francisco and then connecting to Mexico City. It is all on one ticket with United Airlines. I am confused about a couple of things as this is my first trip via SFO.

1: Will my baggage be automatically checked through to CDMX or will I have to Collect it and re-check it.

2: I have a 2 hour delay, will that be sufficient time for the transfer.

3: If I have to re-check my bags will that be just to a drop off or do I need to go to the official desk for United.

4: What happens if I am delayed and miss the connecting flight to CDMX.

Any other advice would be appreciated. John.