I guess Mac will do as a tertiary OS.
Well, c'mon now. Are you just trying to please Suitcase or do you honestly want to experiment? You should probably boot it in a virtual machine to see if it could be what you want. (True for any other OS for that matter.) I always find that anything below the primary OS becomes very rarely used and extremely experimental; after all, do I want to really think hard every time I boot the system about what OS I want? The primary one will quickly become configured and loaded and more likely than not will be the one you use 99.9% of the time. So unless you're a software developer (are you?) I can only imagine that a "tertiary" OS is going to float way down and be ignored except when someone or some situation calls you specifically to it.
I made a promise to run Linux mostly because I got scared of the whole Conficker business. I also bought a new laptop and put 4GB of RAM in it which prevented Windows XP from installing. (Blue screen during setup.) I had avoided change out of laziness. I finally went cold turkey back in March with Ubuntu and have not gone back since. I personally enjoy the full ability to customize Linux systems, and really find it incredibly usable. It still has some situations that require a bit of command line work, but the command line is far less required compared to the way it used to be... and, of course, a great deal of hardware support and availability of precompiled apps is always a blast.
I've never used Mac OS X and have no opinion of it. I suppose I should try it just for record, but currently am very happy with where I'm at. And if you find Windows does everything you want, and you don't have any other objection to it, there's no reason to even install Ubuntu. If you just want to play with wandering around a Unix like world, do a virtual machine or install Cygwin or something.
Some of the software on your list either has a Linux native/equivalent or could possibly run under WINE. It's definitely helpful to have a machine to test the latter on first. I will admit I lost a few programs I would prefer to have due to no Linux version and no WINE support.
Truth be told, I've been tired of Windows for a while, if for no other reason than they always charge so much for it, and then now they do the whole "activation" thing and Windows Genuine Advantage and whatever... but it always did what I needed, and will have the greatest support. If you're not committed to really trying to change how you use your computer then I don't see the point other than the occasional check-it-out with a VM.
