When I was combo feeding, my LC recommended that each ounce should take 5-7min in a bottle because that's close to whay it would take at the breast. If taking longer, you might need to up the nipple; if shorter, downsize it. If you're doing bottle only, then it's less of a concern and just follow baby's cues. You'll know when you need to increase the nipple size. You'll see the baby taking in big gulps or getting frustrated at the bottle because it's too slow.
@Ryann I do combi feeding at the moment. She’s mainly breastfed but she’ll have 1 or 2 bottles of formula in the day. However even if she has expressed breast milk in a bottle she doesn’t seem fully satisfied
I would definitely keep to size 0 teat if you're breastfeeding at all. This means baby is having to work for the milk in the same way as breastfeeding so less likely to develop bottle preference
Are you also breastfeeding or bottle feeding only? If you are BFing I would keep the teet at size 0 since that is closer to what it is like BFing. As far as ounces go it all depends on if they are drinking formula or BM