I have a gtx 285, I am planning to buy one monitor in a few days and then over about a month buy a ati card and two more monitors.
Do you think I'll be fine with 1080? instead of 1200?
And if I go with a adapter, I will be able to run three monitors with no loss in quality?
There are very few monitors out these days with 1920x1200 resolution and they are much more expensive than their 1920x1080 counterparts (like twice the cost). I would definitely go the 1080 route you will save a ton of money with only slightly lower resolution. You will just need an active display port adapter for your third monitor when you enable eyefinity (like $25 at newegg).