WHAT NEXT? NOW IT´S ELECTRICAL.........

Is the earth cable from the engine/gearbox to the car body sound? If you’ve got power to all the ancillaries, the battery + and - connections would appear to be okay. However if the starter won’t turn, then it would seem that there is a fault in the circuits involving just the kit bolted to the engine.

On my 2004 Rav there were several fuseable links in the one unit on the positive battery post.
To eliminate an earth issue you could put a jump lead from the negative battery terminal to a good clean earth on the engine or preferably a starter motor mounting bolt if it's accessible ?

I think I read a post somewhere about someone who fitted an up-rated starter moror to their RAV.
The clicking sounds like a faulty solenoid? And as you've tried, but I'd still add an extra earth strap from battery to engine and to bodywork. An auto-electrician might be the best bet.