It definitely was not sex. The sin was disobedience. There is no reason to think that the fruit was an apple either, as it is only referred to as a fruit. Some say it was a fig, assuming that they would take the closest foliage to make cloths. Most would say that it is not a fruit that exists now.
There is nothing wrong with enjoying sex. In the one of the epistles (I forget which, but could look it up if I had the time) it says that withholding sex from a spouse for any reason (except prayer and fasting, end even then only a prior mutual agreement) is sinful, while using sex for comfort and emotional closeness with your spouse without any regard to procreation is presented positively. Song of Solomon appears to speakof cunnilingus (using metaphors instead of being so crude to say it directly) in a positive light.
Adam and Eve definitely were married. It was the first and archetypal marriage. True, there were no human authorities to recognize it or add anything like an actual marriage contract, but the lack of ceremony does not make it any less of a marriage. Hesed love is the defining quality of marriage, not those traditions.
It was between 4 rivers. One of them is believed to be in Ethiopia, and we really aren't sure about the last one. One theory is that Eden was really big, so the whole middle east was Eden. I've heard that there is a reference in Psalms that strongly implies that the fall happened at the sire where the Temple of Solomon was later built.
I'm not quite sure how rivers are supposed to survive the deluge and the great geological changes that created mountains and emptied the water from the flood into newly created Ocean basins. Perhaps the rivers were completely different, and just happened to have the same name.
I believe that it is thought that the outside world did exist, and that humanity was supposed to work to make the outside world become just as paradisaical. It wouldn't have been nearly as harsh as after the fall, but not as perfect as Eden so that humanity had something to do. Work is good, but backbreaking labor a result of sin.
It is often thought that in the 3 days between Christ's death and resurrection he was ministering to those in Sheol, so that we can expect at least those old testament characters who faithfully performed sacrifices and kept the law to have been redeemed then and to be in heaven.
o well, its all a money scam and polotical scam anyways
More people have died in Wars and conflicts in the name of ''GOD'' or ''RELIGION'' than all other wars combined