Food ------ more than just DOC, Jester got mice, quail and rabbit (he only ate rat if he was really hungry and i wasnt too keen on skinning and gutting them either when he was to young to eat them himself) Smaller owls that dont eat rabbit wont necessarily need rabbit though
separate freezer for food ( unless you have a very understanding household that dont mind having bird food in the freezer

)
an aviary might not be quite essential in the early days but wouldnt hurt to be ready in plenty time to save a rush job of building it when the time comes.
if you intend hunting then a dummy (relevant to the owl type) is handy to start training as soon as they are capable of running towards it and jumping on it which also helps to get them used to the tradeoff from as young an age as possible.
will maybe add more when i remember