If you throw too many features into this project, you risk
(1) Making it too complex to use,
(2) Making it too expensive,
(3) Making it buggy with features that don’t work properly,
(4) Making it a niche product that few people will buy.
Honestly, I’d be happy with a Nitecore SC4 that had a settable charge termination voltage, and lower default charge rates. Nothing else needed.
Or a Liitokala Lii-500 with settable charge termination voltage. (The Lii-500 has a discharge capacity function already.)
Perhaps approach a company with something very similar already, and ask them to add the extra couple of features into an existing product. That should make it easier to build, and less prone to quality problems.