Disney Rookie - need some basic guidelines

[Canadian Rookie]

Hello all. Our family is planning our first trip to Orlando in April of this year. Any online research I do seems overwhelming. We will have 6 non-travel days to enjoy the area's attractions. MK and Seaworld are on our must see list. Do we spend 2 or 3 days at MK? I'm thinking 1 day at Seaworld, and one at Universal. I would also like a sight-seeing/relaxing day if possible. I don't want to be rushing the kids (5 & 9) out of parks because we "have" to be somewhere else. Are there passes we can buy to bypass lines, etc? I would appreciate any help/advice possible to get me pointed in the right direction.