Would advise against changing pH,hardness level's without fair knowledge of what/how products that do this, work.
Of the fishes you mention,, only the neon's would appreciate a bit softer GH ,the other's,,would be fine.
I would not place the number's of fish you mention, 40 +,, in 50 gallon tank and would maybe forego the neon's which in my view,,are not at all,, the hardy fish they used to be year's ago.
If you are set on the neon's,, I might see if fish store would hold these fish for you, with perhaps small deposit for a couple weeks, and if they are still fairing well in dealer's tank after this length of time, then perhaps they will adapt to your water if it is close to same as that in dealer's tank.
The barb's,khulii's, danios,and shrimp, would be fine in my opinion without any altering of water.