Well, everything seems to be working! If something is missing, I haven't run across it yet, despite those error messages. I can boot my computer and when everything is done starting, I can say "Alexa, run Sling TV" and up it pops in a Chromium (Linux) window; which was what I wanted. I haven't tried to find things that don't work yet, as I am enjoying those that do!
As to running automatically, I simply added a command in the Linux Mint "Startup Applications" list with a 25 second delay:
triggercmdagent
That puts an icon on my status panel. If I right click it, I have options for:
TriggerCMD.com
Background Service
Start Background Service
Remove Background Service
Text Command Editor
GUI Command Editor
Quit
I have not done anything with those two Background Service controls as things appear to be working as I want them to.
Thanks for the great support!
Monty