I'll start with the tip:
To set a wrap width (the column at which to wrap text), you set the attribute
wrap_width in your Preferences.sublime-settings file (preferably in the User-specific file):
// Set to a value other than 0 to force wrapping at that column
// rather than the window width
I myself combine this setting with the ruler setting:
The wrap width is nice to have when you're writing stuff that easily spans several lines (in my case this became a problem when writing LateX).
The reason I'm posting this is because I've seen some people searching for this setting by using the terms "right margin"/"margin", which will lead them to the attribute
margin which only sets the left margin.