To add to con-pilots advice, if using Universal, you'll need a hefty bank balance too, not just a good routing
No, Universal is not cheap nor are any of the other international handlers, but if you try to do all planning, including overflight permits and landing permits, and something goes wrong, they would have been cheaper at twice the price.
Never the less, do carry a lot of cash, you'll need it no matter if you use a handler or not.