Learning endgames

So, I havnt done much endgame study in the past.
I decided it is the best way to improve at this point (1800 fide) and am beginning to learn them.

I decided to begin with pawn endings, which I think is logical as a starting point, as most piece endgames should be based around these concepts.

However, at what point should I decide that I know enough about pawn endings and move onto rook endgames?, which are also of huge importance?

i am in the same situatation. I think just going through endgame books that are setup like a course study that have tests at the end of each chapter

Not sure how to help you other than to recommend an endgame book. Check out Dvoretsky's Endgame Manual 2nd Edition. ISBN: 1-888690-28-3. It starts you out with basic pawn endings and advances through to more complex endings. Comprehensive instruction from pawn endings, to opposite color bishops, to bishop vs knight, to rook endgames, to queen endgames and everything inbetween. It's 323 pages of instruction, not including the solutions in the back. If you don't mind reading chess notation (at 1800, i doubt you have trouble with that :D), then you will love this book. He gives great commentary on the games and has exercises to test what you're learning. Hope you can improve!