Don't bother with Sea World.
You need at least 1 day off in three from touring. Do NOT attempt to visit 8 theme parks in 9 days or whatever.
We stayed at Wyndham Bonnet Creek, 2 bed large apartment 1500sqft within Disney gates. Lots of pools, hot tubs, barbecues, etc. www.wyndhambonnetcreek.com/ Ignore the rates on there, the rooms go fro about $120/night, check ebay, hotelclub.com, vacationupgrades.com or farrellsvacations.com Timeshare place, so cheap, they will try to get you to an 'orientation tour' 'resort tour' or 'welcome breakfast' or similar on arrival, just say 'No thank you I've been before'. They also might phone the room to try and sell timeshare, I put the phone on silent.
You can park for free at Magic Kingdom by going round the back entrance.
Tickets, never buy combined Disney/Universal/Seaworld tickets, they are just a bundle of tickets you can get cheaper separately.
For Disney you either get a 14-day UK-only Ultimate pass for about £230, which covers the water parks and the indoor arcade Disneyquest, and allows park hopping, or you get a US 'Magic your Way Base' ticket, which is valid for 3,4,5,6,7,etc. days in 14, with no water parks, no Disneyquest, and no park hopping. 7 day ticket is $263 e.g. here www.undercovertourist.com/orlando/attractions/tickets.html, which is plenty.
For Universal the 2-park £80 UK ticket is probably the best deal, unlimited admission for 14 days, although in reality you probably won't want more than 2 visits there, one per park.
Wouldn't bother with Seaworld, too many theme parks to visit as it is.
Car rental is necessary.
It's necessary to ruthlessly plan which days you go to which parks as the queues are ridiculous, usually worst around 2pm-3pm at the Disney parks. At Disney if there are special events that don't run every day, such as Illuminations at Hollywood Studios, fireworks at Magic Kingdom, the parade at Magic Kingdom, and so on, the queues for the rides will be worse that day. Days with 'extra magic hours', when they open earlier and/or later for Disney guests will also be more crowded. Generally speaking avoid these days. Obviously if you want to see the special event you need to go to the park, but you DON'T need to wait 2 hours in a queue for Space Mountain. What you can do is either 'park hop', just seeing the show but spending the rest of the day at a quieter park, or if you have a 'Magic Your Way Base' ticket, you can't park hop but what you could do is have a down day, just relaxing in the pool and then turn up just in time for the show.
You can view actual wait times for rides at touringplans.com/ and on your iphone. Disney operates a system called Smartpass, whereby you go to the ride and put your ticket in, and it gives you a time to come back and skip (most of) the queue. So many people do this that the normal queue scarcely moves on some rides. Do it as much as possible. For certain rides, such as Toy Story Midway Mania (which is awesome), the Smartpass tickets are all gone by mid-morning or even earlier. The most dedicated would be at the park at opening time, run to the ride, get the Smart pass, then get into the normal queue, ride the ride, and then when they'd done that, the Smart pass time would be ready, so they'd use that go on again. After that they'd just point and laugh at the people waiting 2 hours to get on using the normal queue.
To get an idea of which park will be busiest on which day, this site: www.easywdw.com/category/calendar/ is best.
You can gawk at the Disney hotels for free, take the monorail around the various resorts. Watch the fireworks from the beach at the expensive Polynesian Resort.
All the Disney tat is overpriced but the Downtown Disney Store is still quite impressive. Visit the Disney outlet stores at either Orlando Premium Outlets mall to buy it cheaper.
The Disney restaurants are pretty much hideously overpriced and not great, stuffed with people on 'Dining Plans'. I would ignore them, $300 for lunch with Snow White (somewhere in the room) is not worth it when you can meet her for free with park admission.
Free parking is available at Magic Kingdom using the back entrance: www.themeparkinsider.com/flume/200910/1490/