The best place to look for tractor trailers for sale is on Truck Paper, a company that hosts used trucks and trailers around the world. Their website allows buyers to find listings of sellers selling tractor trailers.
You should insure any vehicles you have, including tractor trailers. You should carry insurance on them even if you are buying them to sell to others because otherwise you will have to pay yourself for any damage to them.
They still are.
Yes, as long as it has some value
This site looks promising http://www.nexttruckonline.com/ they sell trucks, tractor trailers and accessories/maintenance items that you would need for your tractor trailer.
Most trailers are 102" wide. Anything beyond that requires an oversize permit.
No, there is not.
That depends on the size of the tractor trailers (they come in different sizes/models). and how many roadways you will need to get them on/off the land.
There are several tire store in the area too choose from.You can find a limited selection of tires for tractor trailers in Milwaukee at Sears.