Sounds like a very sensible plan! =)
I would still favour aiming for the water parameters that the shrimp you buy have come from though over what someone said on Youtube as the shrimp may be quite different. At least match the water initially, then slowly change up/down to what you decide is the optimum.
Not to labour the point about inaccuracies of TDS meters, but please be aware that there are still variations between meters and unless two people have the exact same make/model of meter calibrated with the exact same calibration solution, then readings may still not be comparable. You're going to be in the right ballpark with your calibrated meter though of course, just don't ever be fooled into thinking a TDS meter is "accurate" in any real sense. Why? Because there is no way to measure TDS directly in such a device. What they measure is electrical conductivity and they then apply some notional factor (usually dividing by 2.00 or 2.05) to convert EC into an approximation of what the TDS of the sample would be if it was saline solution (which of course it's not). Temp affects this calibration factor - some meters have temp compensation (i.e. slightly different factors applied depending upon temp) whilst others don't (same factor applied irrespective of temp). This is why SS give instructions based on EC (uS) rather than TDS (ppm) - EC is an absolute measurement, TDS is an absolute measurement multiplied by some random unknown factor.
One thing you might want to try with your GH / KH liquid tests is to double the volume of water in the sample. Each drop of reagent then equals 0.5dH (rather than 1 drop = 1dH) so you can double the resolution of the test kit. Probably a bit unnecessary, but if you're looking to get an exact standard RO + minerals formula, then might be worth some experimentation, especially with the KH value.
For the 200 TDS water, the GH was 9 and the KH was 3.
9+3=12, 12x18 = 216ppm, so pretty close to your TDS measurement
For the 150 TDS water, the GH was 7 and the KH was 2.
7+2 = 9, 9 x 18 = 162, again not far off.
I would suggest that your GH and KH test kits are reading a little on the high side, assuming we are confident that the TDS readings are good. Why? Because SS minerals are GH + KH + a small amount of other stuff. So your TDS reading should always be a little higher than the (GH+KH) x 18 calculation. You results are the other way round - measured TDS is slightly lower than the calc'd TDS, which can't actually be the case.
I use SS GH+ and my TDS measurements are about 20% higher than the GHx18 calc predicts. I would have thought that the SS GH/KH+ minerals would be similar so that your actual TDS is higher (not lower) than the calc'd value. (I'm subject to all the same errors and uncertainties as you of course with my "calibrated" HM Digital meter and API liquid test kits!).
Realistically, all these values are within scope for neo's. Just if you want to be super-precise then it's good to understand the potential error and uncertainty involved!