that looks ok to me i dont think any can cross breed. i would go with a 20 gal tank long is always better than tall and all should do well with a ph of 7 or a bit higher so you shouldnt need a buffer substrate gravel or pool filter sand will be fine. as long as you have lots of mosses and other plants you should get lots of bio film for them to eat
I can't say but IMO this wouldn't be an attractive tank. Too much going on with so many shrimp. I personally like a single species or two that compliment each other. Three tops if you are really cramped for space.
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