I wash every 3 days and my usual load is about 13 nappies (but we're still using disposables overnight, to appease my OH, but that's soon to change). Of those 13, about 1/2 are bamboo, which takes longer than a day to dry. So by the time all my load is dry and back in the drawer, there's probably at least another 7 dirty nappies in the bucket.
We started with cloth when Adam was 1 month old, and fortunately for us he's never been a frequent pooer (1 a day), so he's never needed to be changed more than 6 times a day. A newborn would go through more, hence why many first-time cloth mums don't start till the first few weeks are past. (As a first-time mum per se, I needed to feel I had a grip on everything else involved before complicating it with more washing!)
I have 31 nappies. Of those, 2 I have stopped using because they always leaked (microfibre), 4 I've put in my emergency bag but don't use often because they're a bit too small, and 3 I haven't prepped and used yet because I don't need them yet (I have enough in size 1 so these extra, which are all in ones ,I am saving till we need them). So that's 22 in my working stash and I have never run out. It's only the bamboo that doesn't dry quickly, so as long as you have a few quick driers (I find my BumGenius V3s are great) you're fine. I reckon you could get away with 20 to wash every 3 days, maybe with a couple extra for emergencies.