Great questions Dave, I'll attempt to answer as best I can from my experience.
So, as you pointed out, stropping post shave helps clean the edge of any residue that might be left following the shave and will dry the edge off and help prevent any possible oxidation. As well, anytime you strop, it's a sharpening tool, so you're in essence doing a very gentle post shave re-fresh on the edge. Stropping prior to the shave further refines the edge prior to your shave.
IRT using fabric (cotton, linen, irish linen, nylon, etc...) prior to the leather, this will, again, clean the edge off of anything that might have accumulated from the last time you used it. Doing this prior to the leather can help knock out any possible burrs so the leather is more effective at refining the edge. In my experience, the leather will also help make the edge a bit more smooth, or at least knock some of the harshness that might be present in the edge.
I personally do not use the rough side of the leather, just the smooth. My normal stropping routine is as such:
Pre-shave:
5-15 laps on turkish linen (cotton)
20-25 laps on irish linen (firehose)
40-60 laps on Kanayama leather strop
Post-shave:
12-25 laps on irish linen (firehose)
20-40 laps on Leather
Generally, I do many more laps pre-shave than post, as the post is mainly to clean off the bevel and somewhat get the edge back to a baseline of keenness. The edge will be further refined prior to my next shave with that razor through my pre-shave routine.
As far as over-stropping goes, you can't really harm an edge in my experience from stropping too much if every lap is done correctly. However, the more laps you do, the greater the likelihood that you do a poor stroke and roll the edge or nick your strop as your arm gets tired. I try to keep the lap count pre-shave under 80, but there are times when I've gone as many as 200 laps on leather. This is primarily after I've finished giving a razor a refresh on the stones. When I do this, I'm very much concentrating on form over speed, remaining very cognizant of whether my arm is getting tired or not.