Hi everyone, new here. Looking for some seedling advice. Ive heard various thoughts on when to separate seedlings.
1. Separate as soon as they can be handled. (And what size is that?)
2. Give a year to fully root then separate.

Thoughts? Also, should i got from potting soil or right to an akadama mix for them?

Thanks

First things first: they need to be outside or they will die, whatever you do.
Second:do not think of them as bonsai but as young plants, so everything you do the first 5-10 years is purely horticultural care,nothing bonsai-ish. So dont go buying expensive fertiliser or soil, just normal potting soil and regular all purpose fertiliser will do.
So, if you can handle them and it seems if they dont have enough space in the pots you can repot them, but be carefull not to disturb the roots. If you can just wait till autumn, they will be bigger and going into dormancy.
Horticulture first- bonsai last: you need a healthy tree to make a bonsai out of whatever you are growing.

There are those who cut the tap root at an early age, like at one year. I don't know much about this but I am getting ready to learn because I have a large number of maple seedlings and I may want to do this next spring. At the same time, they encourage spreading out the remaining roots thinking about future nebari. Again, I don't know much about this but am getting ready to learn.

A standard technique is to put something flat underneath the roots to encourage them to spread out wide and shallow rather than narrow and deep, which is what they probably evolved to do.

All of this would be done in the spring when new growth is just developing. For me that means late February to early March, probably, but the trees will tell me.

April or May, don't worry about it. Let them grow untouched, all next year. Then think about it.