Rather than try to follow specific quests in a linear manner, if there are no clues given or obvious next steps, try just exploring.
Ishmashell is only involved in that dialog; your character just have to decide what to do (throw him back in the ocean or keep him).
For the murder mystery, start with the crime scene, then look for the body (try the morgue, or the graveyard), and that should lead to other things to look into.
You can learn crafting recipes from books, or just by experimenting to see what will work.
There are several crafting guides, such as:
http://www.seth-dehaan.com/divinity_crafting/http://steamcommunity.com/sharedfiles/filedetails/?id=546088017http://www.irodemine.com/divinitycraft.phpEarning a honest living (newbie friendly)