No. If you happen to remember the level of the monsters you can extrapolate it, but either way maybe just try out the highest one you have in your inventory and see how it goes? It should only take a few minutes to finish.
3
Can you see the tier of the last nightmare you completed? | Spyke
There is a calculator here that should give you a good idea https://diablo4.life/tools/nightmare-dungeons
This is glorious
No. If you happen to remember the level of the monsters you can extrapolate it, but either way maybe just try out the highest one you have in your inventory and see how it goes? It should only take a few minutes to finish.