Date picker to update overtime spreadsheet

Guy's
I've got this spreadsheet that i need to change. Our timesheets now need to go from the 1st to the last day of the month (30th,31st etc) How get the dates in rows b to change according to the month in I4 and show only the 1st to last days of that month.

Also this may be a little more complicated , How do i get the spreadsheet to automatically work out time&half hours and double time(sunday) hours. Obviously the positions will change depending on the month.

thanks for you help.