Problems With Disney World Tickets At The Gate?

We are going to Disney from December 8th to the 11th. We are not staying on the property (just off of it, in a house).
We will go to Magic Kingdom, Universal Studios (right name?) and Sea World. We have 7 adults and 3 children.
It seems to us that multi-day passes and/or park-hopper passes will not help us. Is that right?
Big issue: should we buy tickets before we arrive. If we do, we will have to decide on which days we will go to each park (right?). If we do not, we will have to buy them at the gate, and this might lead to long waits. Do you think the waits would be long given our dates there?

Orlando Theme Park Gate Prices?

I am trying to find out what the gate prices are for the following tickets.
WDW Magic Your Way 10 day park hopper with Waterpark option.
Universal/Islands of Adventure 1 day, 2 park ticket
Sea World/Aquatica ticket that gives you up to 14 days.
I already know what the deals on the websites are, what I need to know is what I would pay if I just purchase at the park. I am specifcally looking for the WDW information. The 10 day ticket is offered at any gate right? I can just arrive at any of the Disney theme parks and purchase this ticket from a booth?