Try not to stress. It will be fun!
We've been to Disney Florida and Disney California several times.
I've never prebooked anything, other than one time we were there for halloween so I prebooked tickets to go to the halloween evening event.
Unless you want to eat in the expensive restaurants or have a particular place you want to see/eat at then there's plenty of fast food and snack places everywhere. You can also bring your own food so if you have a villa taking some food and drinks with you will help save money.
For us it is all about the rides. I recommend the guidebook 'The unofficial guide to walt disney world' by Bob Sehlinger and Len Testa.
It is useful in terms of planning your day and how to beat the worst of the queues and comes with useful lists of what rides to do in what order to beat the queues but also has different options for if you want thrill rides, have young dc etc.
They also have an app which lets you see how busy the parks are and how long the queues are.
As well as the rides there are also lots of shows, parades, and meet and greet things to do. So if your dc/you are into that then knowing what's available and what you need to book or where to go can be helpful.
If you prefer just to wander about at will and aren't bothered about getting autographs and meeting princesses, or eating at a specific time, then you can do that too.
Fast pass is your friend so do read up and take advantage of that.
And make sure they know if it is special visit (your first time, someones birthday etc) and get a badge and wear it - not sure if they only do that if you are staying in a disney hotel though. The cast memebers may dish you out with extra fast passes if you are wearing your badges.