Once fish are added you’re going to see ammonia first, long before anything else. If you haven’t read up on it yet please do some research on the nitrification cycle. It’s perfectly safe to do a fish-in cycle if you know what you’re dealing with and deadly (to the fish) otherwise.
A hardness test would be a good idea, it doesn’t hurt. Once again knowing what you’re up against can make a huge difference in you’re overall experience of fish keeping. If you have really soft water (low gh
) it can be easily susceptible to ph swings which alone can not only kill fish but crash the cycle and most certainly kill the fish if you’re not monitoring water quality closely. On the other end of the spectrum a harder water typically has more kh
or buffering capacity and is more ‘stable’, but an extremely hard water is not a good thing either, especially for certain critters!