First things first-Welcome!
IMO A villa would be better because you will need down days,space to relax and facilities to keep the kids entertained-mine loved being able to go in the pool or just chill out watching the telly or playing in the games room-we found that we never relax as much in a hotel room.
August is hot-we prefer May we are fortunate because we get 2 weeks at Whit.
Having searched around I would recommend this site for tickets,villas and car-you will need a car.
If you search around these forums you will find a shed load of suggestions as to itineraries but one thing I would say is build in some "do nothing" days or you will need another holiday at the end of it-you won't be able to do everything so I wouldn't try.
Magic Kingdom at least once is a must-beyond that the world is your oyster and I have no doubt that you will be inundated with suggestions.
Enjoy the planning-I would get my flights first, then search the villas on here,then car and tickets-If next May is too soon or expensive try October=If you are restricted to Summer hols I would go for the end of August as US schools are back.
Enjoy and don't be overwhelmed the people on here are very helpful=ps I am not a villa owner just a user