+1 - Buying these parts as soon as you see them on a good deal means you don't get tempted to spend the money on other things while it builds up and buying these parts early won't mean you are missing out on big new technology - as these components aren't changing too much.
For the other parts (CPU/mobo/SSD/GPU) only buy them when you have all your money (so you get the most up-to-date and best value components - since they change so much). At the moment the best option IMHO for a good value system for gaming music production is a Intel Sandy Bridge i5 quad core CPU (ideally the i5 2500K so you can overclock properly) and Z68 chipset board. However, the intel Ivy bridge generation CPUs are expected to arrive late next month, so by the time you come to buy these parts these CPUs (and new boards) should be available.
Though if you want to get the system up an running ASAP then you may consider running a board which allows you to access the onboard graphics (like most Z68 boards) and put off buying the graphics card for a month or so - this will allow you to run your system and do music production work - but won't let you play modern games, which will need the graphics card.
Similarly, you could put off buying the SSD for a month or two so you can get the CPU/mobo earlier. This will require you to install the OS and other software on the HDD, and to do a re-install when you eventually get the SSD.