There is no particular safety zone when it comes to not getting pregnant. Even if you just had a period and you have sex you could still get pregnant. No one can give you a magic number of not getting pregnant. To prevent pregnancy don't have unprotected sex.
Most people ovulate about 14 days before your next period. So if your period is between 28 and 32 days you ovulate between 14-18 days after the start of your period. Sperms can last 48-72 hours in the uterus/vagina. periods last about 5 days. So unless you have an extremely short cycle its impossible to get pregnant.
It is possible to get pregnant at any time in your cycle. Typically, a woman ovulates (is most fertile) approximately 14 days from the first day of her period. However, sperm can survive for days in the fallopian tubes, and if a woman ovulates early, it is quite possible for her to get pregnant shortly after her period ends.
The time you get prgnant varies for every woman. The only way to be certain if you are ovulating is to take an ovulation test which you can pick up at the store by the home pregnancy tests.
Yes, it is still possible. Although it is unlikely that you are ovulating right after your period has ended: the fact is sperm can live for several days in your uterus!! Therefore they may be "hanging around" should you have an early ovulation. Your chances are remote but a chance is still a chance.