You know how cold you get in different temperatures, so its really up to you...but I think my whole family wore some kind of long sleeves almost everyday when we went at the same time of year. Bring a jacket if you're out at night or early morning, brrr! I even brought a beanie hat and scarf, but I get cold much more easily. (Okay so the scarf was also just for fashion's sake but...
)
I always layered a tshirt over a long sleeve shirt everyday I was there. For MVMCP I wore a sweatshirt; my mom wore a sweater over a TURTLENECK (she gets colder than me sometimes!)
Just use your best judgement given the average temps and whatnot, but no need to go overboard.