If you want to see all the shows and attractions in Sea World you need a full day or close to it, so I wouldn't suggest doing that park on your first day. Go to IOA on saturday, even though lines might be long you should be able to see most of the attractions. I don't know if you know about Halloween Horror Nights but it will probably be happening on saturday and sunday nights.Both USF and IOA will probably close earlier than normal since
HHN starts at 7 pm. Unless you have young kids under 9 or so I suggest going to this event, It's the mother of all Halloween events. Even though crowds get crazy it's a super fun event, I go every year!!
Sunday you should definitely do Sea World since it's mostly shows and just a few rides. Crowds and lines will be heavy at both Universal parks and you will be avoiding this.Also like I said before HHN will probably close the universal Parks early on sunday.You should have a dandy time at Sea World.
On monday you should have the run of the Universal parks crowds probably will be light. Go to USF to start the day and I don't know if you'll have a 2 park pass, if you do go to IOA later if there's anything you missed on saturday.Also somebody mentioned Busch Gardens, I don't think you'll be able to do it on this trip if you're going only 3 days but you should definitely do it on a future trip. It's a beautiful park and yes it sux that they barely ever duel Gwazi , but it's still a great ride along with their other coasters and shows. I don't know if you know about Sheikra the first diving coaster in the US just opened up and I love this ride, Montu is still my favorite coaster in the park , but Sheikra give a great ride!!