AAAHH The joys of learning about cruising!

Welcome! You came to the right place that is for sure! I am fairly new to the
Disney cruise line but have sailed others like Norwegian, Princess, Disney and Celebrity and in theory they are pretty much the same.
The price of your cruise includes:
Your stateroom accomodations with a host or hostess that cleans it for you every day and also gets it ready for you to go to bed at night. This includes putting down the bunk bed that pulls out of the ceiling if you have a room like that, various towel animals, chocolates and the next days Navigator (tells you what is happening each day)
You get your meals which is pretty much all you can eat anytime and that includes room service (usually all you give is a tip to the person delivering it to you), soft drinks in the sit down restaurants, pizza, hot dogs, you name it.
Entertainment which are shows, movies (at the theatre right now type movies not some show from the late 80's).
On a
Disney cruise they have 3 restaurants and you rotate between them. You go to a different restaurant each day and you are assigned a table number which is the same in all 3 restaurants as well as a server and asst. server who also rotate with you through the dining rooms. There are 2 seatings a late and an early. There is also Palo which is an adults only restaurant and it costs I believe $5.00 per person (which is supposed to cover the tip but you can tip more). If you do a 7 night cruise you do all 3 restaurants twice in a rotation.
The stateroom issue is one that is a matter of personal preference. Some like the family staterooms that have a verandah and can sleep your entire family. We did that and it had a couch that was made into a bed and a bunk that came down from the ceiling as well as a murphy bed that came out from the wall. Not all the family suites have the 5th bed. We found it to be ok for 5 of us but have decided to book 2 lower category rooms that connect so you get 2 bathrooms, 2 showers and 2 rooms. Some people opt to go the parents on a balcony room and the kids across the hall..it seems to be a matter of what your family would like.
The best time of the year...well I've only done Disney once but I think the highest prices are at Xmas, the week between Xmas and New Years, Spring Break and I think most of the summer (might be wrong there). I think if it were me I would go to the Disneycruise.com website and plug in different dates and room options just to get an idea of what times of the year cost for your family.
Hope that starts helping!
Heidi