If I were interested in micromanaging the tanks I would start with high quality testing supplies at home. Then, whatever was not in that kit/set might be a target for lab testing. Especially if the lab was expensive. Better to spend some money getting supplies that can be reused, so trends could be monitored, not just a one-shot test.
I would expect to find NO3, NO2, NH3/NH4, P, Fe, GH, KH, Ca, pH, and TDS available in a high quality product. If keeping shrimp or snails is the goal, then a copper test would be high on the list. (I do not know if one is available)
I think it would be good to test for K, also. I have not looked for this one, but I understand potassium is one of the harder ones to test for. Might be worth getting a lab test done occasionally, if a home test is not available.
The other thing I would look into is this:
If there is something that you suspect in the water or soil/substrate that may not be common enough to test for so that hobby (or higher than hobby quality) kit is not available that would be something to test for at a lab. This might include things like pesticides, or other things.
The next level of testing would try to answer this question:
OK, so the tests revealed high levels of X.
If I use this filter media or a certain treatment to remove it...
How many liters of water will it treat before I have to rejuvenate or replace that media?
