What are the advantages of a multiple column grid?
Some advantages of a multi-column grid is that it creates flexibility. The more columns you create the more flexibility the designer has. In a one column grid there is only one area you can place text, but with a more than one column you can neatly organize the text in one corner and it self have balance.
How many characters is optimal for a line length? words per line?
50-60, 12
Why is the baseline grid used in design?
They create a common rhythm to unite the article.
What are reasons to set type justified? ragged (unjustified)?
Justified creates a clean square shape to work well with a grid.
An unjustified body has one clean edge but still respects the organic flow of how the text works.
What is a typographic river?
An area of white space in paragraphs created by alignment of spaces.
What does clothesline, hangline or flow line mean?
Hangline: a column on either side of the body that gives insightful information that is an important side note.
Flowline: horizontal lines that break the page into bands.
What are some ways to indicate a new paragraph. Are there any rules?
You can either not indent and leave space between paragraphs, or you can indent each new paragraph and not leave space between each line. 
