All of the above.Start with grounds and take the Starter off and clean and bare the mating surfaces between the Starter and the engine.This is a main current path when starting.
Check main grounds @ the battery and frame.No point doing in-bike tests on the R/R if there's high current corroded contacts.
Remove check and clean and de-corrode the main R/R connectors.These are commonly overlooked and quite often have never been serviced and a common area of fault and can put a massive strain on other electrical components and in extreme cases cause melt-downs and electrical fires,
