Please help. I am scared about pumping (long, sorry)

Hi everyone, I usually lurk but I need some guidance. I tried to break it down so if you only have advice about certain parts you don't have to read this ungodly long post.

 I was going to wait to go back to work because pumping isn't as easy as I thought it would be for me, I was very lucky that breastfeeding came very natural to me and my baby so it was a surprise to me when I did not feel that ease with pumping. But my boss just called and made me an offer I can not refuse, he said if I would come back to work even just a few days a week and take a pay cut for awhile he would pay for my schooling then come work for him full time of course. We also could use a bit more income coming in. 

 My job is only 6 hour shifts but school would be from 9am to 5 pm at least 3 days a week. It would be like going back to work full time between the two and I am panicking about being away from her that long. I know that it is more important to do this so I can keep a roof over her head and healthy food on the table than my selfishness of wanting to be with her all day but I worry about her even when I only leave for a few hours and I know she is in the capable hands of our family.

 Some of my Fears:

 I am afraid to create and over supply while building a stash and I am afraid my supply will drop once I go back to work. And I am afraid I wont be able to build up a big enough supply before I go back since this is so short notice (No dates have actually been set yet). I fear work and school won't let me pump. And I fear my lack knowledge about pumping (and I have read so many websites).

Right now I pump only once in the morning to start building a stash and I stopped for awhile because I noticed my supply increased and I saw some green poo which seemed to be because she wasn't getting enough hind milk. I started to block feed and it went away. I pumped again this morning since I panicked about my stash after they called and I got 3 oz where if I used a heating pack I could get 3-5oz a boob before. 

-To build a stash should I continue pumping in the morning or should I increase the amount of times I pump?

- If I pump more to build a stash when should I? Do I have to worry about E not getting enough while feeding because she cluster feeds a lot as it is (I think many times its just for comfort because she will take nothing but my boob)

- How did you figure out how much you baby eats? I left for a few hours today and she took 3 oz and then almost another 3 about 15 min. later. Is that okay or normal?

-I am scared my supply will drop. How do I make sure it doesn't? I want to pump during the day but breastfeed when ever I am with her, I love breastfeeding and I want to hit a year at least which is why I am panicking.

-Will a cooler work to keep my pumped milk during an 8 or 9 hour day?

-How long should I be pumping? Until the flow of my milk stops?

-Will I have a problem breastfeeding if I create an oversupply by accident?

-What if they don't give me a break to pump during work or at school?

- I know I am forgetting some questions so please give me all of your wisdom and tell me everything and anything that may or may not help me!