I would also like to know the answer to the first question, but I wouldn't buy insurance until you get to the 75 day out mark when Disney won't refund 100%. Until that time you want lose any money if you cancel.
This depends on WHY you are buying insurance and the terms of the policy you buy. I've had TAs recommend Travel Guard Protect Assist and Worldwide Trip Protector by Travel Insured international. There are difference between these policies, but both provide one free child policy with each adult policy purchased. In addition, they cover pre-existing conditions if purchased within 14 days of booking the trip, and allow you to move the travel date at least once and maintain the insurance coverage.
So the above "you lose any money if you cancel" is true, but you won't necessarily lose the money if you change the dates.
With some policies, "pre existing" coverage applies not only to those people cruising, but also to those staying at home. For instance, if your policy allows you to be reimbursed for cancellation for illness in a close relative, the concept of "pre-existing" also applies to that relative.
To above poster concerned about covering 100% of the cost of the trip....you will not lose 100% of the cost of the trip after your 75 day mark. In fact, I think that figure applies to the last 7 days only (sorry would need to verify this). At 74 days, you would lose your deposit amount only, so that is MUCH less than 100%!
Places to purchase insurance--Insuremytrip.com, squaremouth.com, or your
travel agent.