Allright, Multiple responses, no qoutes. Take what you want.
Was mentioned somewhere in a history lesson that Byakugan and Sharingan have shared origins. Although at the time they said Byakugan was seen as superior so I doubt highly it was Madara who said it.
We don't know if Kyubii is the only beast Madara can control, we know it is the only one he DID control. It's also the strongest. Maybe he can only control one at a time so he chose the strongest.
The ring you see in the Byakugan is the pupil of the user. It is drawn in to show that the eye isn't solid white. Although I do agree there may be a second level. If the two are indeed related than it would make sense that they are both upgradeable.
Rinnegan's true power is the users ability to use all elemental jutsu, not just one or two. We never saw pain use it to it's full potential because what he did do cost so much chakra he couldn't do anything else. One wonders if they had a sharingan/byakugan hybrid. See chakra with 360 degree vision and able to follow all movements.
Sharingan doesn't make jutsu stronger, in the case of chidori, the sharingan see's through the opponents movements making sure the attack will be effective.
Byakugan may become stronger we'll have to wait and see. Aint bad as it is. Could actually beat sharingan except for the Uchiha being able to see the attacks coming and duck out of the way, and 360 vision guarantees genjutsu success.
I mentioned earlier I think Madara may be trying to use Orochimaru's body snatcher jutsu and Sasuke, but maybe he wants Sasuke to get his revenge for him. Currently he can't perform any jutsu, or so he says. If that's the case than he couldn't fuse the bijuu or merge with them unless someone performed the jutsu for him. I don't see Sasuke doing that. And the whole moon's eye plan could be a bunch of hockum based on the fact that Madara said that it's Naruto's and Sasuke's destiny to fight based on the bad blood between their clan's, but if this is the case than is it not also Madara's fate to fight Naruto? He seems to be trying to help Naruto to an extent though. Maybe he's relying on the fight with Sasuke to free the Kyubii, and if that's the case, he may have made all the rest up and his only true goal is to get the Kyubii back out in the open where he can control it.