Im new to wordpress,im trying to build an etsy style shop

Im new to wordpress,im trying to build an etsy style shop ,where users can create their own shops within the site.My questions are as follows:
1)im using the framemarket theme and gridmarket as the child theme which comes with a header thats writtern "GRIDMARKET".how do i remove it or is there a way of downloading it ,edit it then upload it again or is there a way of editing its text without doing the above?
2)There is no widget for registering new users,will i have to do this manually?
3)Also I have footers 1,2,3,4 and 5.Is it possible to add widgets to these as links for example i put a link and call it "privacy policy" then on clicking it all the terms and conditions are displayed.
4)Will all these changes be applied site wide?
5)Lastly,is there some sort of manual/advice for developing an etsy style shop that helps with especially the front end to make it look professional.