cRPG does not have a proper timeline, it has items ranging from very early to very late. Firearms from the 16th century would fit very well.
Nah, Arquebus seem's too out of place. However, like I said earlier, an early hand cannon wouldn't hurt the atmosphere
or balance.
Early hand cannons for the win! Would be VERY inacurate, slow reloading and a bit more powerfull than an xbow.
Since they would be so inacurate, you could get some clans using them in volleys, which would be quite cool to see. Not nearly as cool as longbowmen shooting in volleys though.

Edit: Those gun models are from 'Knights: the last battle' mod if I remember correctly. Screenshot's taken in my little native mod.