plastic trays or better would probably be nursery pots (or similar somewhat deeper pots, since you want room for
roots to grow). if you catch them in the spring when leaves are just starting to open and transplant them then, generally the roots are grown
enough to be relatively robust but will also separate/untangle pretty easily. you can probably do a single-nut layer of acorns across the whole area of the pot, that then gets covered in around an inch of soil. it’s how i do pawpaws (which notoriously don’t like transplanting but i haven’t had trouble with), and other stratification-needing tree and shrub seeds. pretty easy, good results.