Welcome to the club!
Adding copepods to a new tank could be a good idea but the impact could be similar to cleaning teeth: Brushing + Flossing have 95% impact, Mouthwash 5% (or no impact at all), the latter would be the equivalent to copepods.
BRS wanted to sell the Galaxy Pods from Algae Barns, so not sure how credible their experiment is.
If I wanted to add pods, I would add amphipods, though. This is the cheapest place I found for amphipods:
https://www.irwinsbugs.com/. These might have a bigger impact, if any.
However, the question is if you already do all the basic things for maintanance, lighting etc. A tank journal would be great to give you more holistic advice, which could potentially save you money and fix your issues quicker.
Lastly, diatoms might actually not be a bad thing to have. Often, these make sure you are not getting nastier things such as dinos. So keeping them in at least in the beginning could be seen as an insurance.