I don't normally think about the seven sins that much. It is a categorization of the roots of 'human weaknesses' as defined by theologians, whose foundation of belief lies in the 10 commandments and the bible, naturally. As for the degree of the sinning act, it can affect your salvation (catholics believe in faith based action, and that faith alone but contradictory/lack of action is hypocritical). Like anger is one of the seven, but if it is conducted to a degree of 'grave sin' like murder, you have stained your state of existence to 'one that hate so much and even lead to destroy other's life', a state of spiritual reality that defines you and will stay with you forever (aka hell).
Speaking of condition of God's forgiveness, the critical criteria is true repentence, which only the one asking for forgiveness will know if it is there. And you can never 'outsin' God's merciness and think that you have gone too far, for who believe in Christ as God's manifestation of forgivenss will believe that the single act of crucifixion has done away all the sins, including those that you will commit in the future, and these of future generation, if repentence follows. Of course, counting on God's unlimited forgivenss and think that 'let's keep on doing it till later' is not very wise, since repentence can be a very difficult task, especially if it is done with full knowledge of act and consequence, and one is at his/her own risk.
Confession as catholic christians believe is one of the institution set up by Christ along with communion, matrimony, etc. I can tell you that it is not an easy thing to do for me. I am not going to say (and not believe) that those who are not christians or christians of churches without cofession will be refused the ultimate life. I believe that God will forgive the real contrite sinner, but, going to a confession gives me a 'strange' sensation, if prepared properly. I can say that I am kind of independant psychologically and couldn't care less what others think about me, but after some confession sessions I can immediately feel something inside me that can be compared to the smell of oil and I feel lighter, and the blood is cleaner, and then I am at another starting point. I don't know if it makes much sense to you, just trying to share some feelings and experience

.