sponge filter with air hose should keep everybody safe.You'll need an extremely fine mesh filter cover along with a cover on that power head. I recommend buying some filter mesh on Amazon, especially the ones that are bags with drawstring. You can put those around the filter intake and the power head.
You can separate the momma, wait will she release the babies, remove the momma and gradually increase the salinity.As stated, Amano shrimp need to have brackish / saltwater as babies and then transfer to freshwater when they grow up. This is a difficult task as it involves capturing the baby shrimp which are extremely difficult to see and then transferring them to another aquarium you have setup. The only good way to do this is by using a breeding net that is fine enough to hold the baby shrimp. You can then capture the baby amanos and transfer them to a new aquarium. However, you will need a new aquarium setup. I don't know the parameters off the top of my head.
Any shrimp larvae yet?My initial idea was to hatch in the spare 10 gal then add salt directly but the more I read, the more it sounded like transferring after hatching to a breeder tank would be easier. Biggest problem I foresaw was what to do after they've become shrimp? My other fish would feast on them in the main tank. This approach also has the advantage of me setting up another tank after I promised myself not to do so.
For the shrimp tank itself, I'm thinking of going filter-less initially but am still worried about water flow. I have a spare elite mini and plan to stuff it full of a fine filter pad. Would this be sufficient to keep the fry out of the filter? Or is a sponge filter really the only way to go?