Well, not sure I can answer your question directly, but let me share my experience. I started with 30 in a 10 gallon tank. Pretty much just fed them and let them go about their business. I also added some java moss attached to a few pieces of mapane wood. After a couple of months, the java moss had grown so much that it almost literally filled the tank. I decided to move it all to a 30 gallon. So, I went in and pulled the java moss and wood apart and pulled out each piece. I then started netting out the shrimp. A conservative estimate would have been about 800 or so shrimp, but could have been more. I've still got them in a 30 gallon and I net out a dozen or two every other day or so to feed to some of my fish. It doesn't dent the numbers. Once they get to breeding, they multiply pretty quickly. But, there are no fish in this tank.
Now, I've also got java moss in the tanks with the fish that eat these. In one tank, it doesn't help them survive. They are all gone overnight. But, in another tank, they were managing to survive as long as they stayed hidden away. Depends on the fish and how fast they are, etc. These shrimp aren't easy to catch, but if your fish are interested enough and persistant, they don't last long.
So, my answer to you would be if anything in the tank eats these, I think they'll have a hard time getting established. You might want to just set aside a 10 gallon tank and let them breed for a bit. How many to get? If you can sex them, 2m/2f should be enough to get things started. If you Google it, you can find info on how to do that. You could even look for one that's carrying eggs or young. I would be hesitant to put them with any cichlids or any fish big enough to even try to get one in it's mouth. My fish go bonkers over them. Make sure you've got some type of moss for them. The willow moss should do fine. I don't think the other plants are going to protect them much.
I hope that helps. I just brought a group in for my 6 gallon office tank. Interesting to watch. Easy to care for too.
