Which layout to print
Blank is the plainest: numbers and rules, nothing else. It is the one to use if the calendar is going to be written on heavily, or if it is being handed to someone who will annotate it themselves.
Holidays marks the eleven US federal holidays and prints the name inside the day. Notes replaces the empty lower half of each cell with two writing rules, which is enough for an appointment and a reminder without the cell becoming cramped.
Sunday or Monday
US calendars conventionally start the week on Sunday. Most of Europe, and the ISO 8601 standard, start on Monday, which keeps the weekend together as a pair of columns at the end of the row.
Neither is more correct. If the calendar is being shared with people used to the other convention, the mismatch is genuinely disorienting, so it is worth matching whoever will read it.
How the holiday dates are worked out
The dates are derived from the statutory rules rather than transcribed from a list. Thanksgiving is the fourth Thursday in November, Memorial Day is the last Monday in May, and so on, computed for each year.
That matters for the later years: a table typed out by hand goes stale or picks up an error that nobody notices until the sheet is on a wall. Holidays that fall on a weekend are shown on their actual date, not on the observed federal day off.
Paper and margins
Sheets are proportioned for US Letter. On A4, which is narrower and taller, the grid is fitted by height and centred, so the printed result keeps its proportions instead of stretching.
The half inch margin is inside the printable area of essentially every consumer printer, so nothing is clipped when printing at actual size.