There is no definitive answer. They will tell you when something is off. You just need to listen
gH 4 for neos is on the low side of what most people observed. You might try to aim at a gH between 6 and 10. I recently started to measure gH, since I didn't had any molting issues only to find it's way above 15! And that's because I'm a poor herder. I don't have the patience these creatures require and start changing things from one week to another.
Stability is what counts for all shrimp. RCS are more tolerable to quick changes than others. The basic rule of thumb is to change when there's a need for that. It applies to water changes, feeding, fertilizing and what not. If you keep moss, anubias and ferns you won't need to change much and often. I haven't pruned Anubias in my tank since I started it, more than a year ago. Same goes for the java fern. They don't require ferts. Feeding the shrimp is enough for these plants as well.
Nitrates don't affect much RCS, you can keep them in water that has a lot, 40 being the low limit in some cases of heavily planted tanks I've seen with RCS breeding in them. However, don't expect every shrimp, even RCS to tolerate high Nitrates. It's in their genes if they can cope or not. You can get shrimp bred in low nitrates and kill them in your tank. The same that hosts your shrimps without problems. Low nitrates do no harm to inverts. Just keep that in mind.
Also, you might want to develop the habit of keeping them low because you never know when a CRS opportunity shows up and they will drop dead in nitrate levels at which RCS are breeding.
Also develop the habit of drip acclimating things. Drip the water changes as well. Drip everything but the water from your tank
You don't need to measure things all the time. Get the params once then stick to a routine and you don't need to know them from that point on. Unless something else changes your carefully balanced game card castle