1.) Yeah, the prerequisite is basically high school algebra and geometry. You should be comfortable with variables, working with equations, etc. as well as basic formulas like the area of a triangle or rectangle, the number pi, and so on. The book doesn't assume you remember specific algebra topics like systems of linear equations, quadratic equations, or trigonometric functions -- these are all reviewed when they are introduced.
2.) It is about math, but there's a good amount of physics included as well. This is to provide some interesting and intuitive applications of calculus, which could be somewhat dry otherwise.
3.) The code in the book is in Python. The math content is pretty conceptual, and instead of writing down proofs for new math we introduce, we instead write programs that make the concepts concrete.