lol Yeh you can eat carp but they taste 'muddy' and are full of tiny bones so you would have to treat it as you would a pike before you cook it.
Liver flukes are generally from river wcress, the easiest way to get wcress in your pond is to buy a bag from a supermarket and just chuck it in. That way you know its clean.
I did once toy with the idea of making a stream/river and growing my own trout. ;D