How do I prepare shallots for storage please.
Basically the same as onions i.e. dry them off , remove loose skins prior to storing.
I use string bags and just hang them up in the garage
could they go in the potting shed on a shelf.
Yes
A couple look as if they've got mildew. Do they need using straight away?
Yes to the 2nd part
Do not store damaged or diseased bulbs as these may rot the good bulbs.
As you say use them straght away.