Reddit mentions of Basic Homological Algebra (Graduate Texts in Mathematics)

Category theory makes the most sense in the context of other theories. Many things, like Tensor Products, Direct Products, Profinite Groups can be constructed without Category theory, but are best understood via their categorical definition. I would recommend looking at some algebraic and topological subjects that heavily use category theory, then when you want to study it for it's own sake, you'll have a solid background.

I would recommend starting with This book on Homological Algebra since it really emphasizes the connection between Homology, Algebra and Category Theory. After that, you can look at pure category theory and not be lost. Other noteworthy subjects are Algebraic Geometry and Algebraic Topology.