hi steve, welcome to fishlore! i have cherry barbs in my tank and they are fine with a bit of a current. when mine were a lot smaller it was a bit of a chalenge for them to get past the current but once they grew a little it became no problem for them.
cherry barbs are VERY peaceful fish and IMO wont be aggresive to any of your fish (though if they are males they may chase each other when they do there "dance" to see who is the alpha male). im not sure if black neons are aggresive or not but i think the cherry barbs will stay out of there way.
im surre someone else knows more about black neons than i do and will be able to help you more with your second question. if you do get cherry barbs i bet you will love them they are awesome fish.
Good luck
