DD is almost 4 months old, and we currently have 24-ish prefolds, 0 fitteds, 4 PUL-type covers, 2 wool soakers, and 1 wool longie.
I have some AIOs and pockets but I use those mainly for outings.
I use the wool stuff at night and the PUL covers during the day and I think if I had 1 or 2 more PUL covers that would be perfect. Most times 4 is just fine between washings (same as you, every 2-3 days), but there have been times when I've run out due to not getting a chance to wash the soiled ones soon enough, having her soil a few more, and suddenly there are no more covers.
So I think you're on the right track to be thinking of getting at least 6 PUL covers, especially if you'll be doing pockets at night. Just a word on the nighttime, the reason I like the wool soakers (and fleece would be the same I think) at night is b/c anything with elastic on the legs tends to leave little red marks on my LOs legs after sitting on her for so many hours at night. I find that a soaker doesn't leave marks. You'll use your stuffable AIOs no matter what when you go out, so they're certainly good to have around, but if it were me I'd be planning on using the soakers (fleece or wool) for nighttime.
Have fun! I'm just starting to get into the swing of CDing (I'm a first-timer with DD) and the learning curve seems steep at first but once you climb up there and learn, it's so worth it IMO

Much more fun and "good" feeling than those gross plastic things.