You need to decide if you can pay for it all up front or not on your own.
Will you save a significant amount by paying for it all in advance rather than room, tix and/or dining separately? If that savings is more than $100 (the amount you are charged to cancel a res within 45 days) then I would go for it. Also, you have the option to purchase insurance at 59.95 per adult that covers cancellations due to illness, etc. if you have to cancel within 45 days.
Personally, the dining plan cost vs. out of pocket costs for food becomes a huge savings the longer I stay. It depends on where you dine and how often in a day. I know it's difficult to calculate, but just the peace of mind that it's all paid for and you don't have to consider the cost while on vacation is enough for me. You can add the dining plan as long as it's at least 3 or more days before check-in.
As far as tickets go...the tickets are the same price today as they will be a day before you arrive if you are buying 5 days or more with at least one option selected (park hopper, water parks plus or non expiring.) If you are purchasing a base ticket, the price is the same if bought before or on arrival.
Good luck...I know it's seems complicated...if you're still torn, ask questions here and we will help you decide what's best for you and your travel partners.
