Those figures convert to
GH 107 ppm = 6 German deg
KH 53 ppm = 3 German deg
GH shouldn't vary much. It will only change significantly if you use a substrate or decor that is made of calcium carbonate (eg coral sand, limestone rocks) as these will dissolve and increase GH; or if the tank water evaporates a lot and you top it up with tap water - in this case, the water evaporates but leaves the minerals that comprise GH behind and when you top up you add more minerals so GH gradually increases.
KH can vary. The natural tendency of fish tanks is to become acidic. Nitrate made by the filter bacteria (once the tank is cycled!) and other things excreted by fish are acidic. Carbonate reacts with acids and they get used up. If there's not much there to start with - like yours (and mine) - KH can fall to zero meaning a pH crash is likely. This isn't a problem once the tank is cycled as large regular water changes will keep the KH topped up, but during cycling we don't do water changes, and we make a lot of nitrate so KH can get used up.
It is important to keep an eye on your KH during cycling, and I would also keep an eye on it for a while after you have a tankful of fish. And keep an eye on pH.
Back about 10 years ago I was lazy about doing water changes. Sometimes I went 3 or 4 weeks between changes. And I was overstocked as I now realise. Then I discovered that my pH had dropped by a lot so I came on-line looking for a solution, and found Thinkfish. The site had an advisor back then, and he told me it was because of my low KH - at that time my water company used a table which gave both GH and KH. He recommended that I use remineralisation salts of the kind that people who use RO water need, but I found that by changing at least 30% of the water every week without fail stopped the pH dropping.
I did buy GH and KH testers and kept an eye on those for a good while, but once I knew that my water change regime kept the KH high enough, I never bought any more testers once they ran out.