I had similar questions last year getting ready to move from Virginia to California. Studied DOT regs, California regs, Virginia regs. Read everything I could find here on TBN, which is the most practical and thoughtful source of information I found. Made the trip with
B21 and implements on a 14k 20ft equipment trailer (total 8600 lbs). Tow vehicle was 2012 F150 and I used a weight distributing hitch. I was within spec on payload, pulled weight, combined vehicle weight, and tire loading. On the load, I used new G70 5/16 chain throughout and new 5400 lb binders too (I didn't have that stuff before, never needed it). Two chains crossed on the front of the tractor. Two chains, at a 45 degree angle, on the back of the tractor. One chain on the backhoe bucket to keep it from flopping sideways, one chain on the loader (not sure why). One old logging chain wrapped around the two stabilizers to keep them from drooping. Then one chain on each implement. Straps on tool boxes, spare tires, some other stuff. It was a full load and well secured. I was scrutinized by passing highway patrol officers in every state on the six day trip, but never stopped. I did get a walk around inspection at the California border station but no issues were raised there either. I checked the chains every couple hours for the first two days of the trip and had to re-tighten frequently. After two days everything stayed tight for the rest the trip.