Mostly Carnival vs RC? Two other questions!

So my wife and I are looking to travel in January for a 6-8 day cruise and we have a couple questions as I've googled and kind of read different stuff online that is contradictory? Mostly looking for going to Mexico/Belize/whatever else is on the way! If there's another cruise line thats similar please let me know but a lot of the others look either strict or really expensive, or not a lot to do?

I know some of this is ship specific but before I deep dive into those I just have a few general questions.

1. Which of the two has better food in general that doesnt cost extra to get? (be it buffet, guys burgers, or whatever else is included)? is food only available during certain times or do we have to schedule?
2. How would you compare the different companies for general activites on the ship? Like comedians vs shows vs whatever else there is to do? We don't really want to only lounge around and drink, so night activites or water slides would be cool.
3. General vibe between the two? Ive ready carnival is more party like but also not party like for more than 4 day cruises? are they similar?
4. Is January a good time to travel? I assume not over the weekend of the first but i'd guess like starting on the 3rd or 4th would be less busy? Obviously its always pretty busy on ships, that said does one of the two lines more packed by design?
5. Ruins! I think we'd prefer to see Mayan ruins to aztec ones as they sound more intricate and better but other than Chichen Itza (as i've heard thats super, super busy? or theres not much to see other than the one temple? or is it big in general / not as busy as i've read?) which other ones are the most worth while/largest/has the best excursion?
6. How does one get to Galveston if thats the port? Do you just uber from houston?
7. side question, Carnival only has a single cruise in early january? Is this normal//will they post more closer to the date?

Thank you!