In my experience if you have or are willing to invest on the side to gain the necessary abstract algebra background then MacLane's Categories for the Working Ma

In my experience if you have or are willing to invest on the side to gain the necessary abstract algebra background then MacLane's Categories for the Working Mathematician is the go to source. It is certainly "for the Working Mathematician", so don't make bones about that, but to not include it in a reading list is criminal. If nothing else, buy it and keep rereading it from the beginning as a barometer for how much you're learning. As you penetrate it more and more you can judge that as meteoric increase in understanding.