Welcome to SKFA @Etnorb.
I kept an Australian native tank for many years, before letting it go naturally and decommissioned that tank.
I kept Darwin Red Nose (DRN), Chameleon Shrimps, and some unknown Paratya glass shrimp.
Never kept Macrobrachiums however.
I used rainwater predominantly, because it was easiest for me. Rain water without adding additional chemicals to alter TDS, pH, KH. I found RO water to be too fiddly after a while, in order to get it suitable for living organisms.
I collect rainwater from one of my gutter downpipes, it's got a Leafeater plumbed in to strain out leaves and twigs. The water is collected in a couple of 100L tanks.
I would just pour this into the tanks without further treatment. Gets as close as 0 - 1 KH, 60. to 6.5 pH and very low TDS. That's how our natives like it.
If you design/build your tank closely to an Australian biotope, than drift woods and leaf litter will be present in your tank. That will condition the rain water up to a suitable environment for native shrimp.
Fishmosy's guide is great.
There is also a short article on Aquagreen here, if you have not seen it ... https://www.aquagreen.com.au/files/Freshwater_Shrimps_of_NT.pdf
Good luck.