You don't have options with the time you have and if you want to start in New Orleans and end in SF really. What I mean by that is that you could do a loop trip if New Orleans and Texas was not a definite and you saw a little more of the west, or chose more to the east and didn't go all the way to California.

As for rental companies I would shop around on-line and see what deals are available but we have had good deals with rentalcars.com. Are all the drivers over 25 years of age, as that is usually another 'extra' for young drivers.