I don't have my ordered SP20 yet, but want to hit the ground running...
A few questions:
1. Does it tolerate direct PSU power switch off well?
I have never had a problem in switching off via the PSU.. on power up afterwards, it ramps into my pool effortlessly.
Initially, I also had a weak cabling system which tripped a switch on the entire home rig (at that time 1xSP20 1 x SP31 and 2 x S3+)
and when I changed the cables and swapped the required fuse, it ramped into my pool without a hitch.
2. Is there a poweroff "button" in web gui?
Yes, there is a 'stop miner' button.
3. is there a SSH poweroff/shutdown command and if yes-what is it? S3 has poweroff -d [time in sec] command that I find to be much easier on the miner.
I am not sure, perhaps someone else could answer this one
4. is SSH login root or admin? I assume that the password is admin.
ssh is root/root gui is admin/admin.