eh, driving across country isn't too bad, just make sure to have an atlas handy. I'd suggest trying to plan a route that lets you avoid most or all major/larger cities, that way you don't have to deal with traffic coming in and going out of town. You have a lot of driving to do, so just be patient and safe, although if you keep a consistent pace of around 75-85 on the interstates, over the whole trip you will cut a lot of time off of going the speed limit (which increases as you go west).
I think 4 days is plenty of time, i would guess somewhere in the vicinity of 40-45 hours total driving time, depending on a lot of factors. I would suggest just to get damn comfortable in your car, and just start driving. If you get tired, pull in somewhere and either get a hotel, or nap in your car for a couple hours. I'd also recommend either radio or cds that you haven't listened to/don't know (i find that i pretty much know, at least subconsciously, all the songs on my cds as well as the order in which the songs play, so listening to new material or the radio is much more mentally stimulating and keeps you awake much better).
As long as you are cautious you should be just fine. My current "best" is driving from Indiana to Arizona (roughly 1600 miles) in a day (23 hours) solo, i wouldn't recommend that; should have stopped to rest.
Hopefully this was of at least a little help