Treestone
Fish Fanatic
This link discusses it: https://www.researchgate.net/post/How_does_sulfate_reduction_increase_or_decrease_pH
If you are planning on corys sand is a must. Argos play sand is a good choice if you like the colour. As for how much I have seen calculators on some sites, but I like it between 1.5 and 2" deep as that is deep enough to root plants in but not deep enough to cause problems due to anaerobic pockets forming..
Most heaters are badly calibrated. The best way to set them is to go by the thermometer, if it is one that goes inside the tank as the stick on the outside thermometers are not reliable.
I would turn the heater up slightly and see what that does. Then a bit more if it's still too low.
The GH is pretty much what your water company says.
Your water company says your nitrate is an average of 11 ppm over 8 samples, so I would not trust the strip for nitrate.
To cycle a tank you need to be able to test for ammonia. You can buy separate strips for that.
Did you read this on how to cycle a tank https://www.fishforums.net/threads/cycling-your-new-fresh-water-tank-read-this-first.421488/