4lbs of cherries (2kg) should be plenty, i did a fruit beer recently and added 1kg of blueberries to a half batch 11l/3g. seems like its enough.I would recommend using Campden tablets to sterilise the juice and the fruit itself, crush the fruit up and crush the tablet add it and let it sit for overnight. alternatively, I have heard the fruit being steeped in 70 degrees C to remove the bugs
From my memory and what I've read on here, boiling the juice changes the flavour and removes some of that goodness i think, I was just always told to leave it.
The other options with the fruit itself is to freeze it, then thaw it and then freeze it again, then thaw and crush, this breaks down the cell walls and helps releasethe flavour, and kills off alot of the bugs.