i can't help with telling you what to do about LO biting, but i am an exclusive pumper and had the same concern as you. I started a trend and got some great responses that helped me out. this is the link to the trend, if you have time you might want to read it.
I always have the same though looking back. i wish i would have tried harder. i know now that it would have made things easier in the long run, but i needed to make things better at that time and it was either formula or pumping and giving bottles and i really didn't want LO to have formula. I was at a breaking point and made my choice.
i have been pumping exclusively since LO was about 3 weeks (i think) and i have more than enough milk, but i think i might be luck, i've heard of people having problems. the main thing if you decide to do this is to pump everytime LO eats to establish your supply. LO is now 5 1/2 months and i am still pumping and don't plan to stop any time soon. i only pump every 6 hours and still have enough milk, although i don't have as much excess as i used to, i still have enough. good luck in whatever you choose to do.