Yeah, you'll definitely see the topless ones...they're also the ones with the guys in the tight little speedos (i.e. the Europeans). Dark shades are a great recommendation though!
One thing to note, February is a great time to go because it is so nice weather-wise but note that they generally don't heat the pools down there and it is a bit chilly to swim during February.
Getting into the city of Playa Del Carmen is great as previously mentioned and 5th Street is indeed a nice place. You may also want to hit the Ferry and cross over to Cozumel but you don't have a lot of time so you may want to do this the next time.
you'll love your resort and will find you won't want to leave much if at all.
I would also recommend getting private transportation from the airport to your resort rather than the bus/shuttles. After going through customs go all the way out the door...those timeshare people will make you think they are customs people and they'll talk your ear off for 45 minutes before you figure you're being asked to buy something. Stay away...
Other than that, have a great time...you will love it!