Where to start???

You found a tool that does it, pretty much as good as the API allows:

https://forum.renoise.com/t/new-tool-3-0-loop-control/41463

No knob for “Sample Start” as opposed to “Loop Start”

Perhaps you could explain what you are trying to achieve here?

Exotic time signature menu maybe. A tala and raga generator would be cool too. Not sure really…

Off to the warehouse I go…