Ghouls appear only if you spend too much time in one cave section and when they do, they are quite a pain to deal with (one ghoul behaves slightly differently but is still hostile). Ghouls are suposed to be something you really want to avoid. They will get some drops and more purpose once I progress more with the development though.
As for the kobold trader, the entire kobold faction is underdeveloped right now. I will be improving them in december together with the church and militia.