Its already just shy of 64 inches wide and if I had to bet, you will probably add at least 12-18 inches to each side. This puts you at just shy of 8.5 feet wide. As for length, I would play it safe with and get at least a 14 foot long trailer. In my opinion, once you get 14 + foot long, a 2 axle trailer will be much better.
That thing will be wicked with Tracks!!! Make sure you post some pictures!! Good luck and enjoy @DTC !!!