Hey Peter,

Rest assured. There is nothing wrong with this. Actually, I have a nightclub where the entire control system is running on Macs and the very same Macs are running Catalyst.

Everything is run off of iCal which is always open on all machines. iTunes is also always open and so is Quicktime. There are assorted Applescripts and shell scripts which run all the time. Catalyst is always left online and a script is used to bring it to the front and load full screen when the time is right.

The systems are run though a 16x16 matrix switcher which is also triggered from Catalyst. The SAMSC-Lite cuelist (which is part of Catalyst) works nicely for triggering all kinds of events beyond what is running through iCal. A simple MIDI device even runs presets for different kinds of music and different events.

The systems sleep, and control the activation of dormancy all the other devices. The lighting, sound, projectors, computers, and media all run off the same Macs. Because there are three computers and a matrix switch, there is also redundancy in case of a failure.

There are hiccups from time to time but they're taken into account. The systems are even hooked to an external disk for running Time Machine.

Granted the team I worked with on this club as well as the manager and head DJ, know Macs. Even if they didn't though the system is set to work with little need for making changes to the architecture.

The bottom line...
The whole thing works and works fine. Yours can too. The only issue is going to be latency (possibly) or frame drops if QT is running a movie at the same time as Catalyst. Even still, they can all work at the same time if they need to.

I would strongly suggest that you only use what you need to use. I also recommend you turn off anything you don't need to have on. Basic Applescript scripting is something easy to learn. It might take you about a day or so. Write a simple script that says open quicktime and play file. Write another that says quit quicktime. Write even another that launches Catalyst with Catalyst configured to go into full screen mode upon launch. Attach them all to iCal events.

Poof! It's done.
If you have more questions, let me know.