lol...to be honest we don't have these issues...we don't use 3rd party installers...
above is warning, it does not stop script
for 500 enable PS debug mode to get underlying error
and your website support is very clued in with probably wordpress not ecommece per se. few are
I'll be honest we install every version for our labs and have not run into an install issue in a long time...so maybe it's not PS lol