Building expressed milk stash

I'm going back to work in 4 weeks and would like to know how you ladies started pumping to build up a supply beforehand.

My son will be 8 weeks at that time.

Should I pump after every time I feed him? Or leave some time in between?

How many days should I have stored before our first day?

He will be in daycare for about 8-9 hours a day, so I figure he'll be fed every 2-3 hours and I'll need like 12-14 oz a day. Does that sound right?

I will be pumping at least every 3 hours at work.

I'll currently pump each time my husband wants to give the little dude a bottle and I can pump 3 oz in 10 minutes.

Thanks in advance!