I've been dealing with a batch of tinies like Tigger.
Worming and flea treatment is very much dependent on the weight of the kitten. With the real small ones, I take them down to the vet and ask them to weigh. Mostly they need half of a milbemax or drontal, which the vet is happy to help them swollow. They can also have Frontline flea spray which the vet will do, but NOT the pipette as it's too toxic for tinies. Don't waste your money of pet shop stuff - it's for mugs!
He's a tad young to be having food fads.
What did his breeder or fosterer feed him? That's usually a good starting point to establish what his tum can handle.