Meters incorrect readings?

Pan law shouldn't enter into it. We're talking two mono tracks, right? The pan law potentially comes into play when you pan a mono track to the center. Because you now have the same sound coming from both speakers, they reinforce one another and the resulting center-panned signal is 3db louder than when it was panned hard left and right. Pan laws allow for automatically compensating for this 3db gain. Panning mono tracks away from the center would either lower their volume or make it the same, depending on the pan law.

Something else is going on. For starters, if you're clipping on any track, it's probably just too hot. Simply back it off.

If you put a compressor on, that will lower the output (unless you also apply makeup gain in the compressor). So yes, you could have in-the-red signals going into the compressor and under-zero db coming out of it.

The conventional fix is to simply pull the track down using the trim control. However, because you're working with floating-point data signals going into the red zone aren't really a terribly big deal. Just make sure your final output on the master bus doesn't go over 0db and you'll be OK.

No, you're right, the meter should be indicating levels POST plugins by default, although you can configure it either way. Click the little down-arrow next to the meter button on the toolbar and look at the context menu under "playback options". You'll see you have a choice between Pre Fader or Post Fader. If you choose Pre Fader, it's also going to be pre-FX.