First, thanks for the awesome links, those were very interesting readings.

Secondarily, I’m not seeing how the article to which I linked spoke to metaphysics (unless you’re equating metaphysics with a priori principles, which I would find unclear).

Popper felt we need metaphysics. However, he felt we could eventually judge the metaphysics by how well it yield falsifiable theories.

You almost seem to be arguing this yourself above, when you say we need reasonable a priori principles. That seems fine, but those principles could be in error.

Eucleadian math is a good example of something that seemed a priori and true, yet now turns out to be not exactly correct for describing the world.

Check this out:
http://www.unav.es/cryf/theethicalrootsofkarlpopper.html

Follow it up with this:
http://www.the-rathouse.com/RC_PopperPaper.html