Wheel psi/load rating ID ??
This may be true on rv websites but wheel psi/load rating IDs are a big problem on commercial type haulers websites with lots of split bead seats and cracked valleys are the result of using cheap trailer wheels with no max load/psi numbers. Too many folks just assume cause its a wheel.
OP first question.
Never guess how much load a axle carries. You have the trailer so drop by the CAT scales and find your truck and trailers axles loads.
Never go by actual axle loads for choosing a minimum psi from tire mfg load/pressure charts for trailers tires for many reasons. A couple of good reasons is some trailer are heavier a bit or a lot on one side.
Loads on trailers tires change constantly (side to side/fore and aft) and especially strong side winds causing much higher tire/wheel loads on the trailers lee side.
And of course trailer tires side scrub as the trailer is pulled around a street corner or making sharp turns while backing. Tire on our cars/trucks/suvs/vans do not operate in this extreme environment.
Those higher rated load E ST tires are a good choice for 6k trailer axles.
second question.
Run them at 80 psi cold set and don't worry if they run at 90 psi +. Tire mfg know tires get hot from carrying a load at highways speeds...all is normal.
third question.
If its a 6 lug X 16" wheel then their good for 80 psi. Trailer wheel have load rating some where either stamped or a sticker. These can be on the wheels outside/back side or in the valley. A valley load/psi ID requires the tire to be removed.
last question.
Having made a living pulling non rv trailers using the same axles/tires/wheels that come on rv trailer I've had more cheap OEM tire/wheel issues than any rv'er ever faces.
I always sell cheap off brand ST tires/low cost trailer wheels with no pressure/load ID on CL and go with LT235/85-16 E tires like Bridgestone R-238 commercial grade all steel ply carcass on 6k or 5.2k axles. And purchase a known trailer wheel brand that has a psi/load ID or if the wheel mfg can verify the wheels psi rating.
My 32' rv triler has 10060 lbs on 5.2k axles. I use LT215/85-16 E poly carcass tires. I get 50k-55k miles per set and with three sets running with no issues.
"good judgment comes from experience, and a lot of that comes from bad judgment" ............ Will Rogers
'03 2500 QC Dodge/Cummins HO 3.73 6 speed manual Jacobs Westach
'97 Park Avanue 28' 5er 11200 two slides