Pumping questions!

Brittney • I`m 32 years old and have a almost 2 year old son (bday 9/3) and pregnant with our little girl (due 10/4)
Okay my little guy is 3 weeks old and I just started pumping today. My goal is to build up a supply for when I return to work in January and to have some so others can bottle feed him. 
Questions: 
*how many times a day should I pump? My goal is 3...
*if my little guy is cluster feeding should I reduce pumping? 
*How much should I store in each bag? 4oz? 
*if I don't get enough in one session (maybe if I have to end it early), can I combine pumping sessions so each bag has 4oz? Or should I still store them seperately? 
Any help would be great! Thanks!!!