Welcome to the dark side of the force, Luke.
My suggestion for you: Wait till the console bombs in price and pick a Forza 5 bundle up cheap.
By the time this happens, it will be Forza 8, assuming they continue to release a new Forza every 2 years.
My plan is Wii U for 2014, PS4 for 2015, and Xbone for 2019, maybe. Things can change though with a good bundle, and an "arcade" lineup of Xbone's consoles.