The basic Sales Tax rate in Florida is 6.0% and is on most goods and services. The counties have an option, by vote of their residents, to add a surtax of 0.5%, 1.0% or 1.5% to the state rate.
Orange County, which is most of WDW has a surtax of 0.5%, so purchases (including meals) are taxed at 6.5%.
Osceola County, which has the All-Stars Resorts and Wide World of Sports in it, has a 1.0% surtax so purchases at those locations are subject to a 7.0% tax.
Generally I tip around 15%, depending on the quality of the services and compared to my level of expectation for the level of restaurant. At most WDW locations it tends to be closer to 20%. Additionally, anytime I go outside my normal 10% to 20% range I talk to a manager and tell why.