What type of trailer to haul a tractor?

I've hauled tractors on haywagons but that's when I know I can use the back roads. Very slow
haulin too. The spindles on these wagons are low speed types not suitable for highway.

For a highway tandem trailer, you can use surge hydraulic, or electric. If your regs don't specify how many, at least one axle(front) should have brakes. Try to get your axles as close together as your spring spacing will allow. Makes for easier turning and is easier on the rear axle bearings. Some people use 4in channel but I find it will bend in time. But 4in channel that has a truss system above it is stronger. The truss system is handy for side attachments if you sometimes don't want a straight flatbed. Make sure you have closely spaced spreaders under the frame, and at least 2 that are thicker and heavier and span the width and attached just ahead of the front spring hanger, and just behind the rear spring hanger. If you can add a hefty bolt or too at the joints along with the weld you'll have a more reliable and safer joint.

I think you'd want an electric winch or a hand
winch attached somewhere near the front tongue. If hand winch, get the heavier kind with low gearing or else you'll spend a lot of time trying to work a prybar in the crank to get the back wheels of that tractor on the flat. You'll need tie down chains or straps. A corrugated steel truss supported double ramp is handy. The type that's hinged onto the flat and can be swung upwards.

On lights it's pretty well standard except to say don't forget to install the amber side lights
at each corner and not just reflectors. Many a time I've pulled out onto an intersection from a stop to find the guy's trailer hasn't finished passing thru.

Wood deck is usually yellow pine, seal and paint it after a full summer.

I've had mine for 12 years, replaced the deck in year 5 with oak, repacked bearings 1 time, replaced all 4 tires with high load (2 triler tires and 2 load range E truck tires). Mine uses GM bolt pattern rims, found rims were flexing at 7000# (hubcaps popped off on corners) so put on Suburban rims and no more problems.

Brakes on all axles is Mandatory, and you must prove they work. Weighmaster will inspect and ticket will be issues if not functional.

Key is weight and width. I haul 6000# on my trailer, using factory Class 3 hitch, heavy balls, and 7 wire connectors. Stopping is more of an issue than going. Biggest problem was that my Massey had the wheels set too wide and I couldn't get the weight as far forward as I like, but careful driving made it work.

I'd have a wooden deck, like somebody else said its easy to replace. Its also handy if you're hauling something other than a tractor to be able to screw 2x4s right to the deck to help hold the load. I'd do new tires unless the used ones were excellent, I've never changed a tire on a loaded tractor but I'm thinking I wouldn't want to.
I like a pintle hitch for turning tight and for going into places I shouldn't really be, field roads and such, but a ball hitch is smoother pulling and stopping.

I like wood decks because they don't buckle under the load and are easily replaced if/when the time comes.

Tube frames are usually stronger (depending on the wall thickness compared to channel) and provide a built in wire conduit.

As far as tires..... I used a set of used, like new tires for mine and they work just fine. I was able to save about $175 going that route. You can buy tires designed and built for use on trailers. These might be the only choice you have if local laws disallow the use of truck or auto tires on trailer.