Hi! Welcome to the cruise!
We were on the EBTA last May that sailed from Galveston to Barcelona.
The weather was great. I'm not sure it rained much at all. It took us 3 days to get from Galveston to
Castaway Cay. All that time around the Gulf and the Florida Keys were warm. The day we arrived on Castaway Cay it was cloudy, and not all that warm - maybe it was in the 80's. I was a bit surprised that they had the water temperature at 72 degrees. It was a bit colder on our snorkel adventure than I thought it would be, but it was not uncomfortable.
During the 6 day crossing, we had a lot of sun, but it was cooler when you were out on deck. That didn't stop our dinner mates kids from being in the pool most of the time (it was too cold for us, but my daughter (age 5 then - age 6 when we sail this time) had not issues getting into the kids pool). The seas were calm as well. I took a picture one night of the ocean that was a smooth as glass. The only really bad weather we had was the day between Funchal, and Gibraltar. There was a bad storm off the coast of France that was causing us to really rock and roll in the ship - it was not very warm that day either, but it was beautiful when we arrived in Gibraltar the next day.
All that being said, I wore shorts a lot of the first part of the cruise, and pants in the second week, but always had a short sleeve shirt. I'm not sure if that's that norm and we lucked out, but we did have really great weather.
As for the crowds, I think that our cruise was about 70-80% full. They didn't allow any upgrades at port, however. I think they had moved some of the crew to passenger staterooms, as they were already starting some of renovations that were completed on the Magic last fall. We certainly did not feel crowded at all on this ship.
Hope that helps
Chuck