You should keep going until you can't any more, and if you decide it's too much, stop and spend time on other things that help you bond. I've been trying to express / start breastfeeding my preemie for 3 weeks, and we gave up on Friday - it was my health problems causing the difficulties though, and it was taking me well over an hour to express 20 - 60ml (and he takes 50-60ml per feed every 3-4 hours), it sounds like you're doing well and there are no problems with your milk supply. Hopefully your little one will get the hang of breastfeeding, but if he doesn't and you don't feel you can carry on, it is your decision. I found there was a fine line between support and pressure with breastfeeding, so be honest with the people looking after you and carry on for as long as expressing still makes you feel good.
I don't know if it would make any difference to your little one latching on, but I was advised to express after we had tried feeding, so that my flow would be more and there would definately be a good supply while he was trying to feed. On the other hand, the later milk has more calories, so there are probably pros and cons to each order.
Good luck
Carrie