Clearing EPA, how do they usually test it?

If you get busted for not having a cat converter get ready to bend over... And I would not say 'I didn't know I just bought the exhaust online as a package' as it is 100% your responsibility to make sure items you install on your car are legal. You MAY be able to say you bought it like that, but it is still your responsibility to make sure your car is legal so this just depends on who caught you.

If it's possible, get a cat welded in on your b-pipe (try not to modify the headers). Can't remember the exact fine but it is substantial (around what you've stated).

First and only decibel reading was taken from my R33 at 3,300rpm and managed to read not far off 120db.