In that case, I say you get the blue pearls and let them start breeding, and save the CPOs for when you have enough for a few of them. It's quite beneficial to keep shrimp with CPOs, for a few reasons; The cherries get the smallest bits that the CPOs don't bother with, the CPOs help keep the shrimp in check, and the most important reason, CPOs eat their own offspring. Now, that's a lot less likely to happen when there's at least a dozen baby shrimp for every baby crayfish, isn't it? Still best to net them out and raise them seperately, though (And to seperate the larger craylings from the smaller ones, as they'll kill and/or eat the runts).
If you get a lone cray with your blue pearls now, it may end up killing a couple of them before they can start breeding. Better to wait, because the best time would be when there are all ages of shrimp in the tank, therefore there'd be newborn shrimp on a regular basis, not just every couple of months. Higher baby cray survival rate that way.
Edit: Also, CPOs only live a few years. Better to get them all in one batch and have them all close to the same age, for breeding purposes.
