1. And Nagato wasn't able to use Rinnegan to it's full potential.
2. As I said nor tobi or Nagato knows all secrets of Rinnegan, all jutsus and powers and etc.. So It was impossible for Tobi to learn about it from Nagato... Maybe Madara didn't passed down everything he knew ?.
3. For Uchiha like Madara it takes short amount of time to master Rinnegan + he was the most experienced and talented one Uchiha ever, plus he developed it himself and read full Uchiha tablet.. He mastered it perfectly.. Same goes like Kakashi used 20+ years to be used to MS, and sasuke did it in 1year~ and a lot better.. That's the difference between Uchiha and not uchiha in uchiha dojutsu lol..

4. Yes, he knows the same amount as Nagato does, no more. Paths and Gedo mazo are basics of Rinnegan..
5. Ofcourse he knows about Kamui, Uchiha tablet lol ? I wouldn't be surprissed if Madara could do that too, also Yata and Totsuka are legendary weapons, who maybe existed turing his era.
6. Well Tobi's and Nagato's Rinnegan are Madaras Rinnegan, and they both were able to use it - The Original User of the jutsu they possed can use it too, plus he obtained it first, and learned it secrets first so we can easily say it was Madaras summon, just without Bijuus..
Well Madara maybe didn't passed down all the jutsus ? Like Meteor thing or some other jutsus he posses ? You will never know until it's facts, but it's more likely it.. I will say that Tobi is better than Nagato since he mIGHT be Uchiha, but he's nowhere near Madaras level lol.. Madara has more feats and knowlage about it... Nagato has lowest knowlage about it since he's not Uchiha and wasn't able to read UChiha tablet, Madara is Uchiha and read it, Tobi is MAYBE Uchiha and he MAYBE read it.. At any point thats my beliefs, believe what you want, plus Madara and Itachi are both with their Sharingans all the time. :sy: