Zamasu Black seems like an appropriate name for him. There's other possibilities though like Zamaku, Zamoku, Gomasu, Black Zamasu.
Looks like the Fusion is starting out with white hair and a new aura. I don't think he'll have a new form since it looks like Goku Black is going to be in SsjR when they fuse. I just assume his max power will be in this "base form".
I'm not too sure about that one. Super Saiyan White could end up being its official name. I'd rather they just say he has the power of Super Saiyan Rose without the need of a transformation. The name "SsjR" has some nice symbolism to it that I really like, so I'd rather not change it.
If it's normal Potara fusion then he's going to be ridiculously strong. There's two scenarios I can think of. A) Zamasu fusing with Zamasu from a different timeline will result in a "Perfect Fusion" thus giving him a bigger boost than a normal Potara fusion. B) Goku and Vegeta forming Vegetto was said to be an extra powerful Potara fusion because they were polar opposites. This could mean that Zamasu/Black would get a smaller boost since his Fusees are nearly identical.
Either way I can't see a fusion of such powerful characters be weaker than Beerus.
I hope they go all out with the Fusion's abilities. I hope he gets attacks like the Kamehahema, Ki Blade/Projectile Ki Blade/Scythe, and a couple of new ones. Might as well throw in Zamasu's Immortality
AND Goku Black's power adaptation while they're at it!
The power scaling right now from top to bottom is Vegeta-Trunks-Goku right? Or did Goku just get a zenkai boost from nearly being killed by Black? Either way I have a feeling that if the trio attack "Zamasu Black", it isn't going to be enough to beat him. Mafuba just seems like too anticlimactic of an ending for me to even consider. Beerus really seemed to want a crack at Black, and I hope he gets a shot only to be taken down.
(A man can dream) Vegetto or Gogeta seems like the best shot at winning and I sure hope it happens. This villain deserves to face Vegetto.