I would put all the plants you want in now. You will get a good idea what will grow for you and what won't early on. My water is even a bit harder than yours if you can believe it, dKh 19. liquid rock indeed! With water that hard there are some plants you may love the look of that just won't do well, so don't loose heart. Get as many different species as you can and fill it up, than pack it with the ones that do well for you. more plants now will also prevent algea from getting a foothold.
I have to have my C02 set at 2 bubbles per second to get decent C02 levels in my 20 gallon. Any more and the fish are hurting. I'm at around 40 ppm, though my kh and gh test kits ran out long ago, those numbers are kinda memorized as I tested them a million times early on. I just do a ph test once in a while and also use a drop checker for a quick reference on my C02 level. Once you know the GH and KH of your water, all you need to do is a ph test once in a while and keep an eye on your fish for signs of any stress. Unfortunately, you will have to induce this stress at least once to be able to recognize it. Purrbox makes a good point, the City can mess with your water, maybe it's time for me to re test a few things! Your in for a very cool learning experience, lots of good folk here to guide you through it.