Depends how old the "baby" is. Most sources say to feed hatchlings twice a day. As a guideline sometime between 3 and 5 years you can cut back to once a day, then eventually every other day. Usually you will see they don't eat much in the evening so you can cut back to once a day. You need to monitor them and adjust the amount fed as needed to avoid getting too fat or too skinny. They should be well fleshed but easily be able to retract into their shell,

Yes, in terms of nutrition they should be fine. But I fed it dry in a bowl on land. I don’t know if they float or if they will cloud the water. If they don't float you could try feeding it in a shallow heavy glass pan of water (so it doesn't tip). I find very few pelleted foods don't cloud the water, so you'll probably want to feed it in a separate area from the main tank. My 3 inch baby semi aquatic box turtles eat it fine as is, but smaller turtles may need it broken into smaller bite size pieces.

You would have to see if they like it, but it is acceptable for them to eat! :)

Yes. Box turtles are more carnivorous than most aquatic turtles, so this insect based pellet is better for them than many other turtle pellets on the market (including many box turtle formulas)