1. I new game can have a bad disc. There were copies of god of war 2 that skipped the part where you wake up the horse statues making it impossible to complete. Many versions of Jak X had a file corruption issue.
2. It also doesn't matter how new your ps3 is, unless it's in an open area and free from dust it should be fine with not getting too hot.
3. I have completed the ps3 port many times through with no problem.