I'm a tinkerer by nature as well and enjoy experimenting with the fine details of arrow building even if the practical effects may be too small to be noticeable at my shooting ability.
If you want to estimate FOC of a potential arrow build beforehand, Gold Tip has an online calculator based on component weights:
https://www.goldtip.com/Resources/Calculators/FOC-Calculator.aspx
I came up with the following formula based on simple statics. It's probably not quite as accurate as the GT calculator because it treats the combined weights of all front/rear components as concentrated weights applied at the very front and very rear of the shaft. But the formula gives results within ≈1% of the GT calculator and can be put in a spreadsheet to quickly perform multiple calculations and compare potential arrow configurations:
[(front end weight) + 0.5 × (shaft gpi) × (shaft length)] ÷ (total arrow weight) – 0.5