From 30-40K I guess. I'm planning to buy a Focusrite Firewire interface, Protools 11 or probably sonar DAW....
That's a good start. One thing I've been noticing... when you get an interface, make sure it has drivers for the O/S you intend to use. You might get the Saffire, but does it have Win7 drivers? 64-bit and/or 32-bit? What about the firewire interface? You might have to find a particular FW chipset for that. Another thing is motherboards. Do they support your interface without issues? I suggest getting a branded mobo, but getting one with onboard firewire might be expensive, that is if you can find one. Most are jumping on the USB 3 bandwagon - alternative is Thunderbolt, but that's a whole new can of worms. If you go Protools, you usually get the Avid USB interfaces, which at best are USB 2.0, 1.1 for the stereo/2 channel models. It's rare to find firewire interfaces nowadays.
As for O/S, either Vista or Win 7. Win 8 is too new and untested for audio in general, but some have them working just fine - not sure about PT though. You might also want to get those new Haswell procies, but the IvyBridge/Sandy Bridge i-series is fine, too! What I would do, assuming you have the interface already, is get the O/S then look for motherboards and FW interfaces that support it properly. Like I said earlier, go for established brands like Asus, Gigabyte and maybe even Intel or MSI (I've had luck with MSI so I can say its rather safe - stay away from tier-3 mobos, bios support is horrible). No need to get the most expensive mobo; something mid-priced yet has no issues with your interface is what you're after. Lurk in the forums of like interface users to find out what they use.
Then there's ram... 4GB is the absolute minimum for 64-bit Win7. Get good, fast ram - no generics. And get a good branded power supply! You will realize how important power is in keeping your system stable - generics just don't cut it.
I know all these sound expensive, and they are. But you will realize stability is very important over time. Btw, a powerful video card is not recommended when making a stable DAW. Get something in the middle... trust me.