You want to execute the job if it's the 1st of the month and a working day, or if it's the 2nd or 3rd and a Monday, right?
You could write a little script (call it 'wd1') like:
[tt]
#!/bin/bash
DOM=`date +%e`
DOW=`date +%a`
exit $( \
[ $DOM -eq 1 -a $DOW != 'Sat' -a $DOW != 'Sun' ] \
|| [ $DOM -le 3 -a $DOW == 'Mon' ]
[/tt]
Then you could set the following command to run every day (or just the 1st 3 days of the month):
[tt]
wd1 && monthlyjobscript
[/tt]