I assume by theme parks you want to visit Orlando, Florida? I have been several times and I'm going again in 5 weeks so I'll give you as much info as I can!
I recommend booking with Virgin; they're really good and their prices are reasonable. If you visit their website you can price up a holiday which includes flight and accommodation.
I recommend a hotel on International Drive, especially the end towards the Convention Centre (stay away from the Wet n Wild end). Good hotels to look for are the Rosen Plaza, Embassy Suites and Wyndham Orlando.
International Drive has tons of restaurants, supermarkets, shops and attractions like Ripley's Believe It Or Not Museum and Wonderworks. And all the major theme parks are a short ride away.
The majority of hotels offer a free shuttle service to Universal, Disney and Seaworld so you will have no trouble getting to and from the parks. They are scheduled at certain times and they are reliable. I went a couple of years ago and didn't hire a car so we would get the shuttle on a morning then either get the shuttle back or (if we were inbetween the scheduled times) we would get a taxi which didn't cost us too much over the course of the holiday.
If you love shopping like I do then a taxi trip to Mall at Millenia is worth it. There is a Bloomingdales, Macys, Juicy Couture and Victoria's Secret to name a few!
The main parks to visit (go to them all if you can!) are:
Islands of Adventure
Plus there are 3 waterparks - Typhoon Lagoon, Aquatica and Blizzard Beach.
If you book with Virgin or a travel operator they also sell attraction tickets at good prices. Or you can use a website like AttractionTix or OnlineFlorida:
If you did the parks above plus waterparks I would recommend a 7 day Disney pass, 2 day Universal pass plus a Seaworld pass.
For 2 weeks spending money for food, drink, souvenirs and shopping I recommend £800-£1000+. Basically take as much as you can physically save up. xx