Hi,
Here's what I'd say about your main examples.
I can't understand when I have to use week, Sunday, year with THE or without it.Next week, year, Sunday or THE Next week, year, Sunday?
If we are now, for example, on Wednesday, and we want to refer to the following seven days
(Thursday I'll see you tomorrow
, Friday, I'll see you on Friday
Saturday, I'll see you on Saturday
Sunday, I'll see you on Sunday
Monday, I'll see you on Monday or I'll see you on Monday of next week.
Tuesday, I'll see you on Tuesday or I'll see you on Tuesday of next week.
Wednesday I'll see you a week today
Thursday) I'll see you on Thursday of next week.
Best wishes, Clive