Quote 1 says that Lewis does not accept the inerrancy of Scripture -- i.e., he is not a fundamentalist. Since the vast majority of Christians aren't fundamentalists either, this places Lewis firmly in the mainstream. Indeed, such atypical Christian thinkers as Augustine and Basil the Great made similar statements. Hugh of St. Victor wrote a longish book on the various ways of interpreting scripture in the 12th Century.
Quote 2 says that we can avoid sin only through the help of God. The opposing view, called Pelagianism, was deemed heretical in the Fourth Century. BTW, Lewis did not "live with" Joy Davidman, he was married to her. Indeed, the marriage came well before any sexual intimacy, since he originally married her so that Joy -- an American -- could stay in the UK when her visa was not renewed. The two did not live together until she was diagnosed with terminal cancer. See the film Shadowlands for their relationship.
Quote 3, Lewis on Genesis: I have therefore no difficulty in accepting, say, the view of those scholars who tell us that the account of Creation in Genesis is derived from earlier Semitic stories which were Pagan and mythical. This is saying that, like the overwhelming majority of Christians, Lewis was not a creationist.
Quote 4 is merely saying that we do not know exactly how Christ's redeemed us. Quelle surprise!
Quote 5 is perhaps surprising. He is saying that perhaps, instead of going to Hell, the souls of the damned may be destroyed instead. He is, of course, not the first to entertain that idea.