I am going to remove the module so I can start working on the site. What maintenance plugin would you recommend that for sure works so I can work on the site while visitors see a default maintenance page with custom message? I will need to install that before I go to bed tonight as people may be visiting the site from a link published recently.

If you're starting a project from scratch elgg 1.9+ comes with maintenance mode built in.  Go to Admin -> Utilities -> Maintenance Mode

If anyone else has this issue, check to delete your cookies. Website worked fine after that and also when viewing using private browsing mode.

I am going to revert back to the 1.8.15 install however this would be good info for me to know in the future.

If you deleted the data directory then those images and files are gone unless you have a backup or a really savvy sysadmin who can work some hard drive file recovery magic.

Before you rip everything apart and revert though, check that you completed all of the upgrade scripts.  One of those was a data migration script that moves all those files around for the new structure.  If you haven't run that it may be why images are not showing for you.