[I'm another user, though I have not used much of the higher math courses on Khan Academy.  I studied math in college and have done tutoring, but I am not an educator.  Others may have input that is more accurate or useful, but few people seem to respond here, so I'll offer my ideas.]

Yes, Khan Academy has many different courses that overlap or cover the same material in different ways.
Precalculus comes after Algebra and before Calculus.  You can see the topics of KA's Precalculus course by looking at the titles of the Units at https://www.khanacademy.org/math/precalculus; as is usual, there are many topics in Precalculus that were not covered in Algebra.

What will work best for you depends partly on
your math background:

• What math classes have you taken (such as "high school Algebra 1 & 2 and Geometry, community college Intro to Statistics" or "high school Pre-Algebra"?
• For each class, do you still have a good grasp of the concepts, have they gotten fuzzy, or did you struggle with them while in the class?

and partly on your goals:

• Why are you brushing up on math?  Prior to taking classes towards a specific degree?  To get better in a particular field or at a specific task?  Because you want to challenge yourself and keep your mind active?  Because you enjoy math?
• What is the purpose of the compendium (if its purpose is different from why you are brushing up on math)?