[Solved] Upgrade advice?

I would like you folks' advice as you are much more familiar with the steps involved than I am.

I have a very active website running Joomla 1.5.23, Joomdle 0.6, and Moodle 2.0.2
Yes, I know, it is horrifically out of date and MUST be updated immediately. We stopped upgrading when it seemed that every time we upgraded (Joomla in particular) we'd loose the SSO for Joomdle.

I need to save ... everything. Users, courses in progress, etc.

I've updated Joomla sites from 1.5 to 2.5 before, so I have a good idea of the process. (Unpleasant, but do-able.) I have NOT upgraded Moodle, yet.

I'm thinking the first step is to duplicate the site and both Moodle and Joomla databases and get that test site functioning. From there, do you have any recommendations?

I know the Joomla update will break the Joomdle extension -- right? So is that a new-Joomdle install? Should I update Moodle and Joomla independently then install Joomdle 0.9?

Thoughts? Wisdom? Offers of help or sedatives?

Hi.

As you say, I would start creating a new enviroment for testing.

Then, migrate to J2.5 (I never did this, so I don't know how you go about it) and to Moodle 2.x.
As you say, then you will need to install Joomdle again, as the package for 2.5 is different from the one for 1.5.

Thank you! This just gives me a little more confidence as I begin this project!