Agreed. No need to spend time and money on a trailer that has gone through a fire. The metal temper will have been affected leading to a very possible failure down the road if you try and put the trailer back in service.
No interference. Haven't lost bottom at speed. Make sure you don't mount it behind a water pickup, you will get interference from the turbulence of the pickup disrupting water flow around the transducer.
Ken is the man. I run the same prop, OFS4 on my 225, my buddy Smoky, was running it on his 250 before it was stolen.
Good lift, good maintaining slower cruise before dropping off plane, good reverse, just trim up to direct propwash under boat.