Yeah, you can print your boarding pass at home at 24 hours before your flight (the airline will auto-check you in at 36 hours before, don't worry). That way, when you get to the airport you can go straight to security unless you are checking baggage.

You shouldn't check baggage, especially with tighter connections..you can get alot into a carry on. And they usually have laundry wherever you are going.

55 Mins should be ok. But even if you miss the second flight, the airline will get you on the next one, no charge. There are PLENTY of LAS flights! And they are never that far apart.