Hello you didn't told us the production year, but so far as I know there's no issue with a carburettor equipped Royal Enfield Bullet 500, and if all paperwork is good – you've made a good choice here.
Expect the mileage in the region of 25km per liter, although do keep in mind mileage comes down a lot to riding conditions and throttle habits, with major variations possible depending on these two factors.
I have just bought a Royal Enfield Bullet 500, with all the correct papers, but I discovered that the engine is using a carburettor. Please do let me know if this is a reliable model and also please do share the mileage of a Royal Enfield 500 with carburettor.