Hi John,
You don't seem to be getting any traction from anyone else so I thought I'd try to give you some pointers. I was in pretty much the same boat as you until a month ago - though I have previously trial installed gentoo/funtoo a couple of times since the 2000's
Dual booting: I haven't had much luck with the automated boot update being able to chainload windows on my desktop (separate boot disks for window/funtoo) or my laptop (single disk). I haven't had time to investigate what's going wrong so I'm using the EFI BIOS to select the required boot rather than grub.
If you want to play games on your 1060, use the proprietary drivers. This requirement appears to be linked to how you can run steam - see below.
make.conf hasn't been deprecated (or I missed that memo). I still use it for global USE flags, MAKEOPTS, LINGUAS, L10N, VIDEO_CARDS... emerge does a good job of auto updating the /etc/portage/package.* files for package specific stuff (you need to do 'etc-update' and re-run emerge though).
KDE is my old favourite DE and I'm using it again now. When trying to setup your session manager use sddm and logind - I went down a route that didn't appear to be working using some older docs, but the setup instructions for sddm/logind worked for me.
Steam has to be run in some sort of container to get it's 32bit library support requirements met. DR is working on funtoo 1.4 which will allow steam to work in an LXD container, but for now there are instructions on the net for running steam from a flatpak container (I can't remember which container). Worked first time for me using X11, nvidia - just remember to look for some update instructions which have to be run within the container to get the nvidia drivers into it. It takes a little while for steam to startup but once running it's fine. Apparently the drivers inside and outside the container must match.
I'll try to find the specific links to the instructions I used for some of the above when I get time at work.
One other thing... I keep coming across docs (possibly just the one document multiple times) telling me to do an 'emerge sync' to update package lists (needless to say I cannot find it now I want to). You need to be doing 'ego sync' to update packages.