max operational Frequency

Assuming that you're using the "Classic Timing Analyser" (I'm not sure if this applies to Time Quest), go to Processing >> Compilation Report.

Expand the "Timing Analyser" bit and it will show you what has failed - click on the specific parameter to show you the nets.

Yes, these two critical paths will determine your maximum operational frequency.

There are various places you can dinf the Fmax - continuing from above, if you click Timing Analyser >> Summary then you can see there. If you click Timing Analyser >> Clock Setup (or hold) then it will help you work out which paths in particular are a problem.

Don't set your Fmax requirement to be much higher than it needs to be - it will make life unnecessarily hard for the place and route.

Hope this helps