gREEn7o0answered grow question 3 years ago They are still pretty small and could be fine in a solo cup as long as you do your part to keep them happy (watered and fed.) But you could always pop them out really quick to see if they are root bound. Transplanting to a slightly larger pot probably wouldn't hurt as long as you don't put too much water until they spread their roots.
I definitely agree that building a good root system before transplant is beneficial at least in my experience.
I tend to go from solo (I let 'em get about a foot tall) to a gallon nursery bag (until I see lots of roots along the inside of the bag) then usually into 5 gallon bag.
I have seen people go straight from seed to 7 gallon bag with no issues, as long as they do their part to not over water.
