Preemptively welcome to the fold. Ogres are a blast to play in
AoS.
A good discussion of many of the current units can be found here:
http://www.dakkadakka.com/dakkaforum/posts/list/657583.page
In regards to the battalion, it is a great set to get you going. The Tyrant and Butcher are also excellent additions.
Bellowers are a unit upgrade, but like banners and a champion. Traditionally you would have one of each per unit. There is currently nothing technically stopping you from having multiples in a unit currently. Currently being the key term there, as I would expect something to be officially announced down the line. Most of the people that I play with have just made a house rule of one of each command model per unit. In regards to weaponry, unless stated otherwise they have the same equipment as everyone else in the unit. and operate in an identical fashion, save that they will grant an additional bonus while they are alive.
Hope this clears up your questions.