Okay:
Boddynock, taitzu, you're both signed up as alternates. Sorry I couldn't accomodate you as players, but who knows, you might get lucky!
It seems as though the best compromise in terms of levels would be somewhere around level 11, I think. Which on the planar scheme of things would make you players, but not quite in the big leagues yet. A fairly comfortable place to be, I think.
Ferrix, an artificer would be fine. I like them alot too, they're cool. With the levels we'll be looking at you'll likely have crafted some items of your own, so let me encourage you not to stick to the DMG item listings. Branch out, make your own stuff! The item creation rules are pretty simple to get your head round so long as you have a calculator handy, and it really adds perosnality to the character. If you don't want to wade through the item creation rules yourself, tell me the kind of thing you're aiming to make and I can do the hard work for you. I admit that I like political intrigue myself, so there probably will be some involved unless the entire group has little interest in it. That doesn't mean you have to get involved in the politics of course - you can remain aloof from it all and I'll do my very best to keep things interesting for you.
Kangaxx - bear in mind that part of the beauty of Savage Species is the ability to play a monster from whatever level you like and have it pretty well balanced with another class. That said, templates are fun too! Again, if there is anything wierd you want in the way of templates or whatever then tell me and I'll do my best to accomodate you so long as it fits within the setting. And let's face it, most things can be made to fit Planescape!
Isida - I'm afraid I have none of those books, though they're all on my list of things I'm considering buying. Are any of them worth channeling a portion of my very limited resources into? I'd probably rather you just went with the Psion - but then, that might have something to do wiht the fact that Nomads are my favourite kind of Psion and, indeed, probably my absolute favourite class. They rule!

And somehow they seem particularly fitting in the Planescape setting.
As for the 'party of rogues' idea - I think this would work, but rogue should probably be applied in the general, rather than class-specific, sense. A band of unscrupulous wayfarers could work well. Maybe tied by faction as well? A gang of Indeps?
But that is, of course, just one idea. You've got plenty of time to think about it.