Are you going to be hauling this tractor around a lot, or just trying to get it home? Are you planning on hauling it with any large 3pt attachments on it, like say a rotary mower? I have an 18' tandem axle car trailer, and with my rotary mower hitched to my tractor, it overhangs my trailer by a couple of feet. That's with the bucket on the FEL, and the bucket sitting flat on the deck.
If you're only moving it home and done, consider renting a trailer. If you're going to haul it around frequently, get enough trailer to clear the length of the biggest attachment you ever think you may buy for that. Same goes for tractor size. If you ever think you may go bigger on the tractor, get a larger trailer now, instead of having to rebuy the trailer when you buy bigger tractors.
My next flatbed trailer is going to be a gooseneck, deckover, probably 28'-ish, so I can haul my tractor, plus a couple of implements at the same time. I want the deckover to make it easier to load/unload pallets, hay, lumber, or whatever with just forklift forks and less manual stacking to clear the fenders on a standard deck car trailer.