Hi Marianne,
In my opinion, the best route is to make a backup of, then remove your hard drive and replace it with a small SSD, ive been fine with 128GB. Reserve this drive for OS and Apps only. If your MBP can accept it, remove the optical drive and install the OWC Data doubler with a new HDD for your media (when is the last time you put a CD in there?).
Install everything fresh, don’t restore settings from a previous Mac. Of course it’s fine to copy over any individual files you need, by plugging the drive into an external dock. If anything goes wrong, or crucial things are incompatible, no problem, just put the old OS drive back in and continue your work as always.
Out of your listed software, I can only confirm FCP 7 as working on Mountain Lion.
If you do the Data Doubler, you’ll probably need an external DVD drive for all the installs and other uses in the future. To make clean installs a painless process, I’ve been accumulating disc images of all my install DVDs, install files, custom templates etc. and a text document with license keys to a backup drive/USB stick. Just plug it in and start installing everything.
You are wise to be hesitant about just updating everything on a production system, especially one that hasn’t been updated in a while. Many things are likely to stop working if you do so.
Oh, and download mountain lion but don’t install it, find a guide for making a USB drive installer. That way you can install Mountain Lion clean when you put the new drive in, instead of installing over a Snow Leopard install.