yes, you would need to use crontab -e if you like to adjust/edit the user crontab.
yes this is possible. You could have used one of your favorite search engines to answer the question yourself. bash - How to schedule to run first Sunday of every month - Stack Overflow
Following crontab entry should do
00 09 * * 7 [ $(date +\%d) -le 07 ] && /run/your/script