I use two sources of calcium, I have a scatter of dolomite gravel mixed into my substrate and I add calcium to the water with a commercial additive made for reef aquaria. A good place to average is between 5 and 10 degrees of GH, a little less isn't bad, more and you start thinking about african rift lake tanks. Actually you'd need a lot more for that, ignore the exageration.
Nordic is using crushed coral gravel in his filter, but he needs to remember to test regularly and keep an eye out that he doesn't raise the GH level too much.
Yes potassium is a good thing to add to the tank, it seems like most plants need that to do well.
Aquascape? I'm a crypt farmer.
It's a fine line between fishing and standing on the shore looking like an idiot.
That IS an aquascape, it's titled "The Vacant Lot".