I totally agree with MiniBump and Raspberry about breastfeeding. It may be tough in the beginning with frequent feeds, but it's all good for establishing your supply. Even if baby wants to nurse every 20 minutes for hours at a time, the frequent sucking triggers your body to make more milk when your milk comes in. Being engorged in the beginning can be painful, and your nipples might be sore at first, but it gets better quickly -- and from there it's easy!
There's really no need to monitor breastfeeding output -- just watch your baby and feed on demand.
Is he/she growing, peeing, and pooing at good rates? Then all is well! As previously said, formula top-ups mean that your body will produce less milk in the future due to reduced sucking, so that's something to be aware of. The best thing to do if you're worried about supply is to just bunker down and nurse like crazy. I agree with the others -- pumping is a LOT of work, so much more so than just whipping out a boob and feeding when your baby wants it. I'm going to have to do it this time since I might need to be away for many hours if I get a midwifery interview, but I'm not looking forward to it. Also, you get less pumping than you do nursing, so your pumping output doesn't really represent your actual supply.
I just ordered and screened a bunch of breastfeeding books for the breastfeeding group I'm running, and so far here are my recommendations for good starter books:
-Womanly Art of Breastfeeding (as already stated)
-Breastfeeding Made Simple
-The Ultimate Breastfeeding Book of Answers (Jack Newman is awesome and this book is like an encyclopedia and covers everything!)
If you have any concerns, I'd first turn to kellymom Jack Newman (he writes some good FB posts), and a good lactation consultant is indispensable in the beginning.