re: I’d recommend that the installer should to ensure that it the destination drive is accessible, and that it has write permission in the intended directory, and report back if not
I would, however I have no control over the WordPress plugin install/upgrade process.
re: And if the Connections directory already exists, a more graceful failure would provide the user with information along the lines you provided in your solutions.
This is a safety measure enforced by WordPress. I am unable to alter the process or change the resulting error messages.
Again, apologies for the trouble! Glad to hear my instructions helped to get the site back up and running.
ps. WordPress 4.6 might have muched improved plugin installation/update process. YOu can preview it by installing the Shiny Updates plugin. I do not advise installing this on a production site as it is for testing only. Even though installation/updates will be vastly improved, plugins will still not be able to override or change the process. I have not tested it myself yet… I hope one of the things they do fix is improving the error messages as will as instructions on how to fix (the instructions I age your apply to any/every plugin when that error is encountered, it is not Connections specific).
pss. nice site!