Like I said with the right colony cannibalism is almost inexistent (took me 4 tries from scratch to achieve that but I did eventually)
Now as far as starting your hatchlings if you are fine with rats you can always concentrate one that if you have the room to do so but I will recommend to keep a few mice just in case, not all hatchlings will start on rats so unless you have a steady supplier, keeping a few on hands might be a good idea.
I have always kept mice just in case even before keeping colubrids.
Now if you want to keep mice I would start from scratch again don't holdback from animals that cannibalize their young same goes for chewers and biters.