I bought almost all of our prefolds used, so I am not the best source for prepping instructions. We have 24 orange edge newborns and 24 yellow edge smalls. A lot of people advise skipping the newborn size and just folding down the rise of the smalls to fit your newborn for the first few weeks. I have to say, I am SO glad we got the newborn size. Zoe was 7lb 6oz at birth, so not super tiny, and she wore the orange edge prefolds until 6 weeks. At 10 weeks, the yellows still give her plenty of room.
12 of our yellow edge prefolds were new seconds (seconds have slight flaws, but are still usable). GMD is great about telling you exactly why something is a second and the disclaimer for these was that they are slightly smaller and may be twisted after prepping. They are definitely smaller, but it turned out to be perfect for the 2 weeks that she was too big for orange, but swimming in yellows.
Now that we are done with the newborn size, we use them as burp rags, changing pads, and inserts in our pocket diapers. You can't go wrong with having prefolds in your stash, and if you are patient, you can get a dozen used for 25 dollars.
Update - 5 months: The yellow seconds are too small to snappi, but are still working to trifold. I definitely want to get a dozen of the next size (red). I would feel like there was a big hole in our stash if we didn't have some these babies lying around.