Is there a formal discussion of these various approach minimums? I
looked through all the obvious places (AIM, GPS manuals, AOPA
articles), but I haven't found a comprehensive discussion of these.

Example:
My understanding of LNAV/VNAV is that it has a barometrically generated
glideslope. That would mean that any GPS with LNAV functionality should
be able to generate a glideslope if it has an appropriate altimeter
functionality. However, LNAV/VNAV is only discussed in the context of
WAAS (AIM 5-4-5(e)) . If the glideslope is purely barometric, why does
one need WAAS for LNAV/VNAV?

Only a few places spell out what LPV is, but I finally figured out that
it stands for Localizer Precision Vertical Navigation. Perhaps LPVNAV
might have been a better acronym. In any case, I am assuming that the
altitude in LPV is generated from WAAS, hence it is not prone to
altimeter errors.

Finally, if I have the GNS-430, what options do I have to enable these
features? Does the installation need to be recertified, or is it simply
a firmware upgrade?

Any explanations or pointers to other articles would be appreciated.