Just to throw my two bits in even though many of the questions have been answered...
Sometimes you can get group discounts. Not sure if 10 people / 5 cabins will meet the thresholds.
Christmas/New Years is one of the most expensive times to cruise. The decorations on the ship are nice though.
IMO, the standard Eastern or Western Caribbean cruises are ok for a standard 7 day cruise. There are some more interesting itineraries for the Caribbean nowadays.
Cruise Critic is the FT equivalent for cruises. Lots of newbie questions are asked. Lots of cruise veterans to help answer even the most quirky questions (sometimes even better than TA's and cruiselines themselves).
An extremely rough baseline we use for initial pricing of a cruise is $100/person/night double occupancy inside cabin. But that gets thrown out the window for high seasons. One of the more interesting times to book is Wave Season that runs roughly January to March each year. It’s a period where there’s a big push to sell cruises. However, you might see some deals trickle out in December too. This isn’t necessarily the cheapest time to book (as some itineraries may end up being discounted if they aren’t selling) but it’s typically decent pricing but with a bunch of value added perks thrown in such as included gratuities, drink packages, Internet packages, onboard credit, etc.
IMO, I think it’s fine cruising without status. The perks are really nice to haves than something that would impact your experience without them.
Booking through a Travel Agent is nice as they can help identify some of the deals going on, provide you with additional perks like onboard credits (OBC), have blocks of cabins booked to give you a better deal. Alternatively, some TA’s just end up being middlemen and bottleneck you with regards to questions and issues that you need to get addressed directly with the cruiseline.
I’d also suggest trying CruiseComptete. You’ll get quotes with no obligations.
The biggies that generally aren’t covered are gratuities, alcoholic drinks, soft drinks, specialty dining/foods, shore excursions, some activities, etc. If you get enough of OBC’s, it might cover a chunk of your extra spend. Personally, I’d recommend booking/organizing your own excursions since it relatively easy and way cheaper. You just have to be organized to get back to the ship on time. There’s a lot of Do It Yourself (DIY) info on the destination forums on Cruise Critic.
IMO, a newer Royal Caribbean ship will likely fit bill for the wide range of family. Haven’t cruised Disney but it’s a bit pricey but very highly rated. Personally, I like Celebrity. My friends who cruised with us just tried Princess and found it very comparable.
Note: The class of ship within the line is potentially important too as some of the newer ships may have amenities and facilities that aren't/haven't been retrofitted on the older ships.