This is what works for me: I use 50% perlite and 50%miracle grow potting soil (do not use moisture control soil). Hetty mentioned 1 galloon pots for transplanting seedlings. (I grow my seedlings in tiny pots and just gradually move them up 2 sizes bigger if I think the roots need more room or the soil dries up in a day. I have too many, I don't want them to become trees too fast.)
When transplanting seedlings, be extra careful not to disturb the fine roots. If you can transplant with the rootball intact, that would be best. (That's why I grow my seedlings in smaller individual pots so there is minimal trauma when transplanting). I usually dig a hole in the dirt of the new pots first, the size of the hole is bigger than the rootball of the new seedlings, then transfer the seedlings and cover the rootball with dirt. Then I water it thoroughly after applying with 1/4 of the recommended slow release fertilizer and just follow the instruction on when the next feeding should be (usually after 3 months).
I only stake if the seedlings are totally crooked and has not branched out yet . If they have branched out, I let them take their own fascinating shape.
Good luck and post an update. If your weather warms up, gradually introduce them to the sun (partial sun first couple weeks so leaves won't burn then full sun). If your weather this year is warm, You will have 20 small trees by year end.
