Exciting days ahead!!
I noticed you commented about using kalkwasser with ATO. In your case, as you do not have corals, Ca & KH should not reduce as it is not consumed. But by adding kalk, you may be continuously increasing Ca & Alkalinity. Personally, i won't be bothered with pH (don't chase the numbers). Without corals, just use fresh water for ATO.
Regarding biodiversity, don't add live rocks from LFS. They are loaded with pests and risk doing more harm than good. In any case, once you add corals, you will get 'new' bacteria anyway. If you are 'kiasu', just add different brands of bacteria along the way. Microbacter7 is good. Prodibio BioDigest or Fauna Marin Bakto Blend are also other good products.
Regarding the ugly diatom phase, just wait it out. Diatoms are actually algae in a silicate (glass) shell. Don't stir or blow it off. Siphon out the diatoms when you do water change to export them permanently. Phosphate reducing media (GFO, Rowaphos) are known to bind silicates.
The old school of thought from many years ago is to have close to zero nitrate/phosphate (similar to natural sea water). The current common practice is to have slightly elevated levels since the home aquarium environment is different from the ocean. Again, recommendation is not to chase numbers to get close to 0 nitrate/phosphate. Fish & most corals are tolerant. Even if you have 25ppm nitrate of 0.1ppm phosphates, the tank will do fine.