Yes, I do use bamboo terries but not exclusively, I have 4 that I rotate with my Little Lambs & BumGenius. I really do like them, though I need to find a fold that contains poo better than the one I use right now.
It's my good friend ShadowRat who uses terries pretty much exclusively during the day. When she and I were both thinking about cloth, we discussed it a lot and she did a test on cotton terries vs bamboo and found that it's true, they really do absorb a significantly greater volume of liquid. However, the downside is that they take longer to dry. I tumble dry for 40 mins on low and after that they still take over 24 hours to dry hung on a rack in the house.
The thing about flats on newborns is that they can be bulky so if you want to use them from day one you might need smaller ones than you'd need as little as one month later. I didn't start using mine at all till he was 2 months old (used the LLs from one month) and they were fine. I think mine are 60cm squares and they were £3.50 each from the Totnes Nappy Company (they sell them in 50cm and 75cm squares as well). Don't know if that's a good price, bamboo is more expensive than cotton, though.
I also recommend fleece liners, which are available from most nappy sellers - I love the Little Lamb cotton fleece ones, but also have some that are cut from an Ikea fleece throw. They really keep baby's skin dry, if you don't have them baby ends up basically wrapped in a sodden towel if not changed fairly often.
I'd say, depending on how often your baby poos and how often you want to wash, you could manage with 20 and wash every 2-3 days.