> Why do I need to disable a filesystem indexer by default that slows the system to a crawl?

As far as I'm aware, that's considered a thing of the past. I haven't seen it recommended for any recent version anywhere and at least for me, it runs perfectly fine without disabling it.

I also only have one kwallet daemon running right now.

That's on Plasma 5.8.

I think Ubuntu 16.04 is on Plasma 5.7 or older. (That's where I experienced this).

My rule of thumb: don't use Kubuntu, use some other KDE distro ( used to be mandrake/mandriva, now possible OpenSuse or Arch or something, I don't follow it too closely ATM.)