Overwhelmed - feeling like work won't... work?

My plan has been to go back to work 3 days when LO is 12 weeks. We have grandpa lined up to watch him, so it seemed like a pretty sweet gig/no-brainer that I go back. However, as it approaches, it seems almost impossible.
LO still breastfeeds every 2-3 hours day & night, & it takes him 40+ minutes to feed most times. He is a reflux baby, so we have to hold him upright for 30 minutes after eating. He sleeps MUCH better while held, & mostly only stays asleep for 40 minutes if we set him in crib. So, a feed-cycle looks like:
40 min- feed
30 min- hold upright
40 min sleep 
60 min awake; 
(can try to get him to sleep again but it often takes so long its time to feed again)
A 2-hour instead of 3 hour is simply: 40-feed, 30-upright, 40 sleep, repeat.
I also only pump 4.5 oz during a pumping session & this doesnt seem to be enough, so I think I will haffta pump extra during his 40 min naps on the days I don't work.
My husband is AMAZING when be is home & does split the holding upright & awake times. But he works long hours & he needs to sleep too. On an amazing night I get 4 hours & he gets 6. 
I feel like this is schedule is working for us now, but I just feel like things may fall apart when I try to throw working & pumping into the mix?? I feel SO guilty quitting, however. We could certainly get by without me working, but I would feel like I bailed on my boss & I would have a lot of guilt (not contributing financially, not using my education, etc).