Yes, separate colours are a good idea in theory.
However our big'n'expensive Epson always refuses to allow us to change one colour at a time. Could just be our printer, but i have found Epson to be most reliable in the past (more so than Canon).
Agree you should check the prices of generic cartridges when you buy (they may not last as long but they are much better value overall).
Also bear in mind that the major difference between printers is print speed. You won't need a high speed one, but some of the cheap ones are so slow as to be almost useless. Other than that, we have found Epsom and HP to be more reliable than the others.