AFAIK (which is not very far) we process toxins through our livers but don't generally store toxins there, so conventionally reared liver isn't a big problem.
I like my lamb's liver (which is more or less indistinguishable from calves', but half the price) just cooked through: sliced to a bit more than 1cm thick, and fried for a minute or so on each side. Plus a spoonful of home-made stock if I have some, and of course bacon if some 'needs eating', served with pan juices over strongly flavoured salad leaves, like rocket or watercress. I freeze the slices individually wrapped, and I've found I can cook them more or less directly from frozen. It all takes about 6 minutes from start to lunch.
You have the right basic idea for cooking it - not too much. First time I bought lamb's liver, I overcooked it woefully, and got something like boot leather only less edible. I've never tried it rare. Maybe it'd be a thought to find out how you like it before mixing it into something else?