How exactly does the Motronic system calculate fueling?
Very roughly:
Load * KRKTE * req_lambda = injector on time, where load=MAF/RPM
does the fueling that you dial in at "low" boost" carry over when you increase boost?
In most turbo applications the FPR uses the manifold pressure as a "reference", so fuel pressure is constant with respect to boost.
but assuming the MAF is stock should I need to touch any MAF-related maps at all?
Nope. You can leave all of that alone.
Also, the section regarding desired AFR and EGT enrichment tables... can anybody explain in slightly simpler terms what that section is explaining?
In short: ME7 will run lambda=1 pretty much all of the time. There is a built in enrichment mechanism which is based on an EGT threshold. When calculated EGTs go over that threshold, ME7 switches to the "BTS" map. If req_lambda!=1, ME7 goes "open loop" and no longer uses narrow band O2 sensor feedback to adjust fueling; rather, it relies entirely on MAF readings.
There is some debate whether or not this is the "right" way to do lambda!=1 enrich, since there are other ways of accomplishing basically the same thing (i.e. LAMFA).
Hope this helps.