6 nights is fine. I would say that is the minimum to do, but nothing wrong with a full week! :)
I guess it depends on you GD. Is she okay being away from home? If yes, why not the week? Check in isn't until 4pm, so the first day is mostly travel. We first went to WDW with our little one when she was a young 3 years old. We only did 5 nights. She was fine even back then, so we quickly moved to a full week, which is.....travel day, 6 full vacation days, travel day. Yes, you can use travel days for activities, but without a home base, the risk and logistics get more complicated.
BTW, what are your plans for a rental car? Yes or no?