Agree with Colin. And given the information you indicate in post #3 that was given to you by your fish store staff, I would not accept anything they say without confirmation/research.
For example, the bush fish...this species absolutely cannot be kept with anything just because of size. This species is extremely timid, and requires a very quiet tank with no active fish, lots of plants including floating, because it is an ambush predator. The active rainbowfish (depending the species) would not work with this species, and it should also not be combined with gourami or cichlids.
As for water chemistry, this is a very complex subject and the fish store employees likely do not have all that accurate a grasp of it, or they may think it too complicated to explain to customers. Their advice to somehow harden the water to match the stores is very inaccurate and misleading. For one thing, temporary store water may or may not harm fish, but permanent parameters that are substantially different from what the species requires is a very different matter. Ascertain the GH, KH and pH of your source water from the water authority and then select fish suited to that water; this can save a lot of stress on you as well as the fish that have to live in it.