transcooler line pressure

thats a good question but I don't think there is an answer to it. It would depend on line restrictions and the condition of the rear bush in the case.
It is nothing like full line pressure.

The pressure in your tranny lines varies as per restrictions in your tranny... At Idle the C-4 pushes about 14 to 20 psi of pressure. it goes up as the rpm's increase, but I don't see it exceeding maybe 80 psi... I have never seen a need for anything more than a rubber line and a hose clamp to hold 70% of transmission lines in place, and some of them did not even have flared ends to prevent the hose from slipping off. It's best to flare them though for the sake of your own sanity if nothing else....
I believe that 99% of the trans coolant lines that are made of metal are made of metal to increase heat distribution (rubber does not distribute heat very well) and ease of installation....

thanks thats what i wanted to know, my hose is 250psi hose and I am using push on barb fittings with clamps

That will definitely be enough. Good luck!