How powerful would he have been??
Stronger than Sasuke's Rikudou PS, but weaker than his BPS.
I disagree, Lord Madara's Susanoo would be stronger than BPS since he is the Juubi Jinchuriki with 3 eyes.
PS + Juubi Chakra equals something like this
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Which is irrelevant, since Sasuke synched his PS directly with the chakra from all 9 Biju. Unless Madara does the same (which he can't) or infuses his PS with the chakra from all the people trapped in IT, his PS would still be weaker.
Not quite. That's susanoo empowered by Rikkudo chakra+more bijus with rikkudo chakra. Madara already uses the bijus for his rikkudo chakra.