I would recommend taking as many as you possibly can, with being (somewhat) prepared, of course. My testing layout did result in a few more failures than others, but I did complete everything within about 6 months of my 1st passing score. I took the approach of trying not to waste any testing windows. I really did not want to drag this out and put the 18-month deadline to the test. I was a MS student, worked FT, married, and wife was pregnant at the time. So it is doable for sure.
3rd Qtr 2010 - took B (71)
4th Qtr 2010 - took B, A, R, F (74, 71, 83, 73)
1st Qtr 2011 - took B, F (77, 78)
2nd Qtr 2011 - took A (84)
BEC - 71, 74, 77 (Feb - 2011)
FAR - 73, 78 (Feb - 2011)
REG - 83 (Nov 2010)
AUD - 71, 84 (May 2011) - Done!! CPA licensed in TX (July 2011)