Hi,
there's no chance your baby will become dehydrated - lot getting all that milk! It's normal to poo a lot if they are getting a lot.
Sucking is everything to babies - sucking is comfort, as well as food. Sucking also helps them digest their food. However, when babies get a really full tummy of milk, they might want to suck to help comfort themselves - then they get another full tummy of milk and off it goes. some mums find that it works well if they feed their baby as often as they like - but from the same breast for say, 3 hours. The breast naturally becomes emptier - so even though baby is getting all the sucking he needs he gets a lower volume of milk.
Are there any allergies in either side of your families?

Regards
Barb