I don't know if this has been posted elsewhere before, but here we have the Merchant and Great Merchant. I really wanted to see them in battle but I couldn't find any image until now...
Merchant:
Great Merchant:
I think units will depend of which side you choose. Pegs, myrmidons and the new classes seen in the first trailer will be in the Hoshida path. While wyverns, knights, cavs, etc will be in the Nohr path.
Maybe, but I didn't use any of them... I only tried Laguz in PoR and didn't like them... In RD I didn't even use one. I just don't like the idea of Laguz...