I just learned of this game but before I buy it I would like to know if it will have co-op? The problem with Skyrim and a lot of these games is they never have co-op, how hard is it to make like a 4-6 player game?
no , kingdom come will not have any online/co-op .
possibly in future acts if we beg them enough 
The problem is, it is really hard to make a storydriven coop RPG. Its not easy to write a story about a group, because players could spread in several different directions. Warhorse is only a small development studio with a small amount of money, and they have to focus on their core ideas to make a game like this. Sadly there is no time or money to make a coop-modus right now.
So its a single player game similar to skyrim or witcher…
mods will be available