Couple of CDL questions

Hey guys I’m a farmer. Own and drive a truck on a regular basis. Of course I’m not required to have a CDL within 150 miles of home so I don’t. But I’ve been thinking about getting mine and maybe doing a little local driving in the off season. Questions follow:

I’ve heard you can’t take the CDL test in a truck with farm tags, is this true?

Is there any size requirements on the truck and trailer other than it has to be a CDL required truck? I was thinking of taking my CDL test in a little single axle with a like a 20 foot gooseneck just to make my life easier.

Does the trailer have to be air brake equipped or just the truck, and the trailer be electric brakes?

thanks in advance
God Bless

pic is my rig in case you’re interested