1-2. The first pre-labor cesarean section is extremely safe. A second may be safely performed in most cases. 3 or more c-sections are exponentially more dangerous for the mother - with placenta previa and accreta increasing in frequency rapidly. If you are one of the 50% of U.S. Women that will only have up to 2 children, 1-2 pre-labor c-sections may be your best bet - discuss with your obstetrician.
No Certain Number. There isn't an identified "safe" number of c-sections that a woman could have. However, the risk for complications increases with each successive c-section. With increasing number of c/s, the risk for placenta previa and placenta accreta increase. These increase the risk for needing a cesarean hysterectomy. Also higher risk for damage to other structures, such as the bladder.