Hello, Pauly...I do have box hedges and a few topiary shapes in pots. I'm just having a little problem with what you have or intend.
Am I right in thinking you just have pots of box at the moment and intend to use them at a later stage to make a hedge or as potted topiary shapes?
At the mo, I will say that the new growth you speak of should be trimmed back if necessary now while it's still soft, not later in the year. There is an old gardener's saying that says 'trim your box on Derby Day' i.e. the first week in June.
Feeding while still in the pots, I would suggest a fortnightly feed of liquid Growmore during the summer.
There are pest and disease problems, but no need to trouble you with these unless you have an issue with them.
Hope that helps!