Hi bro,
welcome to AQ. Are you going to setup a low tech or high tech planted tank? Why i say that is because moss do/do not need fertilizers nor co2 to grow but it will grow very slow without those. Cold water is good for moss since you say you are using a chiller aswell. For CRS and cardinal tetras i don't think they are good to be in the same tank. Cause tetras will go after them when lights off. So i would not recommended you to put tetras in the tank just CRS will do with some cleaning crew (eg. otocinclus).
As for gravel, any type will do like ADA, GEX or MAGIC soil that will bring down the ph of the water.
Hope these information helps you..
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