We did the trip in April 2007, and it was wonderful trip. Looking at the climatic data, April and October would approximate each other, September being much warmer. Overall, we found the temperatures fairly warm, but you have to remember that the trip covers latittudes ranging from New England to Cuba, giving a very wide range. Actually, even October is warmer than April. We don't remember any mosquitos, so, if there were any, they weren't significant to us,
Breakfasts were typical of hotel buffet breakfasts the world around except that there were addtional asian choices. We don't remember ceral, but assume it was there. I wouldn't worry about the milk. GCT/OAT makes sure that any place that they feed you meets US ssantitary standards. sometimes going as far as bringing their own cook to the kitchen.
We did a blog/tripreport that you can read by clicking here. We would be glad to try to answer any questions, but we would have to reread the blog to refresh our memories.