I'm glad your little guy is better today.
As far as powdered banamine...I've never heard of banamine coming in powder form, only liquid and paste. Are you sure that the powder you have isn't bute rather than banamine? if you have the liquid form (usually given by injection) you can give that orally.
For deworming, our foals get dewormed monthly until they are 10-12 months old, then they get changed to every 2 months like the rest of the horses.