Smaller Water Changes

Smaller water changes are fine, especially if you aren't overstocked. But bear in mind it's not only nitrate that water changes remove. There are lots of things we don't/can't test for that build up between water changes. Having worked in a hospital lab I am well aware that our urine contains a whole host of things and fish will excrete similar chemicals (and we tested urine for a lot of things!) These shouldn't be allowed to build up either. That's why even in heavily planted tanks, if you have a lot of fish you still need to do big water changes.

Your hardness of ~8 is GH, general hardness. That is a measure of the amount of divalent metal ions in the water, and in our tapwater that's almost exclusively calcium and magnesium ions. My son used to work for a water testing company! The thing that prevents or allows pH crashes is the amount of carbonate and bicarbonate ions in the water and GH doesn't measure those - that's KH. And it is quite possible to have a reasonable GH with low KH. I have GH 6 and KH 3.
If you want to be absolutely sure your KH is high enough to prevent pH crashes, you could always ask a shop to test a sample of tapwater. The critical value is 4 German deg/70ppm.