Christians have no obligation to keep a Sabbath or Holy day in the week.
Those under the Law Covenant (the children of Israel) should keep the seventh-day sabbath. (Romans 3:19; 9:4) The sabbaths were a "sign" of that covenant between Yahweh and the children of Israel. (Exodus 31:13) Those children of Israel who become dead to the law through Jesus (Romans 7:1-5) have a sabbath that the natural children of Israel under the Law were not allowed to enter into. (Hebrews 3:5-19) The "Gentiles" who belong to Christ (Galatians 3:28,29) were never under that Law Covenant.
Yes , but no more holier than any other day of the week
That depends on how you look at it it said God rested on the 7th day. The seventh day is sunday
Yes. Thats the day when we stop focusing on work and other things and focus on our worship to Jehovah.
No, because religion=superstition. The Old Testament/Torah is just the folk tales of a tribe of self-important shepherds.