If you were to copy the config file over to a test forum would the both forums connecting to same database not cause problems?

Yes good addition, make sure you edit the config to point to the test database if you are setting up a testboard.

There are a view more things to be aware of when copying your lifeboard to a testboard:
- Change the board url in your vBulletin Options to your testboard
- Members who are subscribed to threads or forums could get mails about updated threads link toyour testboard. Easiest way to avoid this is by disabling the scheduled tasks that handle the subscriptions.
- If you store attachments or Avatars/Profile Pictures in the filesystem, and you have set an absolute path to that directory on your production board, change these paths to point to your testboard directory! (Make sure you are not moving the directory or all filez will be moved from productionboard directory to your testboard!!!)

And probably some more i can't think of now.