Populating columns with days based on a selection

I am trying to build a sleep tracker in Google Sheets (link). The idea is to select a year and a month from a drop-down list in cells A1 and A2, which would then populate columns based on the number of days in that month. I have tried different formulas that I found on stack overflow and elsewhere, but could not get them to work.

In short:

1. I am looking for a formula that will populate the columns with days of that month and a name of the day in a row bellow.
2. Looking for a way to summarize the time of sleep at the end of the each day, based on a ticked checkbox.
3. I am not sure how the year and month selectors should be formatted (as plain number or a date).
4. Is there a way to automatically insert check-boxes to the days of the month?

This is the formula that I have tried to adjust: =INDEX({TEXT(SEQUENCE(1; DAY(EOMONTH(A2&"/"&A1;0)); A2&"/"&A1; 1); {"d"; "ddd"}); {"Total"; ""}})

But it returns with "Error In ARRAY_LITERAL, an Array Literal was missing values for one or more rows."

Please note that ";" is used as an argument separator instead of "," (regional settings).

Thank you in advance!