Congrats my Queen...
I think the Disney cruise is a real quality experience - especially for kids. In trth, I think it is mostly about the kids unless you are an adult Disneyphile (and there are many).
For me, a four-day cruise would work - because it is about the kids and to them seven days is probably over-stimulation.
These ships are VERY activity rich for kids. Adults know how to relax and kick back, but kids will keep going until they drop. I feel like a 7-day cruise might get the kids too worn out.