First off you do not say what your upgrade is from/to and whether you have any kids and I will not assume anything.
As for a 3 night or 4 night, we have always told people interested to do a 3 night just to see if they like cruising if it is going to be their first time. However, I believe the Wish will probably have a lot more kids in July than November if that would be a concern. It will also probably have more passengers since it will still be new and a lot of Disney die hard cruisers will want to sail as soon as they can.
If you have kids, the pools and aquaduck are going to be packed in July. Just those reasons alone could push me to November. That also could sour you away from cruising again. If you don't like cruising, 4 nights is not that much to deal with. It would give you a chance to see how relaxing a sea day is! As EOD K9 said both the 3 and 4 nighters have their pros and cons. For the same amount of money with a room upgrade plus 4 night, I would go for the upgrade.
As for water temperature at Castaway Kay, we were on the Dream for 3 night cruises in September for a 40th anniversary celebration, November, and we were just on it again for the January 14-16 sail. The water temperature in September was about 84 degrees, November 79-80, and the last time was 77-78 degrees. The cast members apparently don't know what the water temperature is or won't tell you but I found this web site to tell me:
https://seatemperature.info/castaway-cay-water-temperature.html
I was one of the few that got in the water both November and January. Was the water cold? YES!! But after you are in for a little bit it doesn't seem to bad! It is doable if you are brave enough!!!!!!
As for the regular weather in November or January, we really didn't notice that much difference.
Good luck trying to choose and let us know your decision!