well now that it's the weekend what better way to spend sabbath than making myself a servant to my inquisitor?
let's start with his/her first question:
Do you believe Sunday [aka, simply not technically, 'first [day] of the week'] is the primary day Christians ought to gather?
let's put some scripture!
the hour is coming when you will neither on this mountain, nor in Jerusalem, worship the Father.
(John 4:21)
... continuing daily with one accord in the temple, and breaking bread from house to house, they ate their food with gladness and simplicity of heart, praising God and having favor with all the people, and the Lord added to the church daily those who were being saved.
(Acts 2:46-47)
ok, so Biblically speaking, i think your question is ridiculous.
Christians -- actual Christians -- don't have any requirement to worship in a certain place or on a certain day.
have a look at Colossians 2. =]