Unbleached Prefolds need to be washed and dried 8-10 times to reach their full absorbency. We only use those, but I believe unbleached is 4-5 times. And yes, I would use less detergent now too as you don't want to start out having build up in the diapers if you use more.
Covers you can wash once and use, so no need to wait on those. I would definitly recommend more covers with 24 prefolds for a new baby though. Probably 6-8 because their poop usually gets on the cover. But if you're waiting to find out the size of the baby first, then get more, that can also be helpful and covers generally ship super quick.
Hope this helps and good luck!
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