Is there a way to trigger an update check and/or confirm if all add-ons are up to date from an external application? I'd like to create a Powershell script that can open Minion, trigger update check, if everything is updated, launch ESO, then when ESO is closed Minion closes.
I would not bother with checking the update state.. just set Minion to update automatically and it will be done before you are logged in. Otherwise you'd need a file watcher for the minion log.. or just parse it every few seconds (oof). You could of course try to run it without the launcher to pipe the Logger directly into the terminal, but that might be too much work.
For autoclose you could make a script that starts Minion, ESO and other stuff you want to run when the game starts and then add an infinite loop that polls Get-Process every 10 seconds or something.
Or you just tell it to kill minion 5 min after it has been opened
No there isn't. You can create a script to open Minion, set it to auto update before so it updates as it is started. Wait 2 mins (updates should not take that long or maybe only at patch days or after it, the next few days) and then lose and run eso64.exe