'way smaller' than the mother bulbs isn't the best sign. It means something wasn't to their liking and rather than producing another big, blooming size bulb they've split up into many smaller bulbs which likely won't flower. They can be planted as deep as before but I'd suggest adding a few new ones as well so you're guaranteed to see a few flowers at least.

You can feed now but better would be to wait until they start rooting so that they are able to 'soak up' the feeding. Without roots they can't do that. Actually in your zone I'm surprised they haven't started rooting already, but as soil temps drop they should start.

When growing in a pot make sure they stay well watered, fertilize more often, and plenty of sun until the leaves die off. Once they dry out or the soil in the pot gets too hot they will go dormant and your bulbs won't grow any larger for the next year's bloom. Tulips are especially tough because the whole bulb regrows each year, things like hyacinths and daffodils just add or lose layers (like an onion).