First, before I go on to what I have to say, is this registered for on road use or is it being used off road such as for farm use and you don't need it registered? If for on road use, you may be violating the vehicle code in your state.
You stated your trailer is 9 tons (18,000 lbs). Is that the weight you have it registered at with your DMV or the Gross Trailer Weight Rating (GTWR) that is on the manufacture's plate?
More than likely you have it registered at 18,000 lbs. I don't know how it is in your state, but in PA don't get caught by the DMV on the highway with that combination and hope you don't have to go on the road side scales. Your trailer will be sitting and you will be driving the Yukon to get the F450 (and depending on what year and package that is, it may not be legal) and paying fines.
The Yukon, if MRBB is correct, is rated to tow 8400 lbs. Right there you are in violation of the vehicle code because the Yukon's towing capacity is much lower than the GTWR. Even if it is empty this truck/trailer will be in violation as the vehicle code goes by the registered GTWR not what it actually weighs at the time of being stopped.
So to be legal you would need to first register the trailer as a 8400 lb trailer to keep it legal when being towed by the Yukon, even when empty.
As for the hitch you have listed, that also will be illegal, because the towing capacity is only 16,000 lbs. You would need to get one that is rated for at least 18,000 lbs. The hitch/receiver/ball combination must be rated equal to or greater than the GTWR of the trailer being towed. Remember when selecting a hitch/ball/receiver combinatoin that the rating of the hitch/ball/reciever combination goes by the lowest rated component. So, if your hitch is rated at 12,000 lbs, the reciever is rated at 10,000 lbs (which the Yukon probably is) and the ball is rated at 7,000 lbs, the overall rating is only 7,000 lbs.
I would not count on the tolls being less because you took the front axle tires off. It is still a tri-axle trailer with that axle hanging under it. I may be wrong on this.
Remember, I am basing my info on PA laws. Laws in other states may vary.