A guiding principle in all this is to get as much mileage as possible out of my current muscle memory.
I never use Alt in the linux world. I never use Del either for that matter. On my "normal" keyboard, Del is way off in the boondocks to the right, and if I am in vi, I just use "x" to get rid of characters under the cursor. I ought to put both of these on some layer of exiled keys. I might (maybe once every 2 or 3 years) do a Crtl-Alt-Del to do a reboot or something, but I am not sure if I ever even do that. Maybe I could define a key macro on some exile layer to do that sequence. Right now I am running Xfce on my linux system and it ignores the 3 finger salute both within a terminal and if typed with the mouse on the background.
It is surprising how little I know about my typing habits and how much I am learning about them now that I am fooling with the Ergodox. I thought I used both thumbs to hit the space bar, but in truth I actually use just my left thumb. So having return hit by the right thumb is just fine and sort of logical maybe. I was going to allow either thumb to hit the spacebar. The lesson here is that the giant long spacebar is some kind of stupid design decision from long ago. Especially given that I am right handed and never use my right thumb for anything in my current typing habits!
I want to completely rework what Ergodox ships as layer 1. I have no muscle memory for it, I am starting from scratch, so anything goes. Getting rid of the numeric keypad frees up the right side for better things. Such as moving +,=,<,> and other such symbols there. My idea is that anything I use often should be one up or one down from the home row.