Greetings there!
Mike from Toronto, Canada here.
Mathew suggested I bid on this project.
Great to hear that you have a mid-sized wiki site! May I have the URL of the site?
I do have experience working with the Open Source Wiki coding; here's how I would go about developing / updating this project for you.
a. Take your live, fully functioning WIKI site and place it on a dev enviro
b. Register the website / source code with Github ( a repository) - proper way of developing new enhancements and keeping track of changes.
c. Place a password on dev enviro so it's not indexed by search engines.
Go through and update the latest versions of the code, if something was to break, as you've suggested - we'd test and handle each accordingly (As your proposal)
I truly look forward to hearing from you!
Thanks and best wishes,
Mike