Hi RegisG,
I saw this question when you first posted it but did not reply.
10 shrimp per gallon is a number that I to have read on the internet.
I don’t think I am any kind of expert but I have been able to keep cherry shrimp alive for 3 years.
Here is what I have done and you can make off it what you want.
I started with 5 shrimp, after a few months I brought 4 or 5 more cherry shrimp just to be certain I had a strong mix of blood lines was my thinking.
I now have hundreds of cherry shrimp ,well several thousand would be closer to the truth but you would think I was full of it.
Shrimp breed easily. It’s unlikely you want to get a male only group to avoid breeding? Shrimp breed faster than MOST SPECIES of fish eat them .
By adding multiple hiding places for the shrimp to moult in .
Adding vegetables for other fish. Doing a normal water change routine as you would for fish. Water changing into a white bucket then netting the adult shrimp back into the tank. Feeding the fish a healthy food once a day. Not cleaning everything and making a sterile tank but allowing a normal healthy amount of biofilm to grow as it is in any tank. You to will have more shrimp than you can count.
I suggest you start with a handful and let them decide how many the tank can support.