1) There are two ways. Either you go into the 7days2die mani directory and look into Data/Config/. There you will see lots of xml files. One of them (I think "quests.xml") is for quests. Edit that. A better way but a bit more complicated way is to code your changes as xpath files and drop them into the Mods directory (that you have to create in the main directory). There are explanation threads here in the forum about xpath, for your first steps editing the files directly might be easier.
2) Data/Config/loot.xml. Read the explanation in XML.txt first, I think there is a paragraph which explains what happens in loot.xml.