Thanks for the response efidm.
1) I would say yes, but I'm not honestly sure.
See I thought so too. But I did some further reading after I posted and found this in the cybernetics section: characters who possess two bionic limbs do not gain double the bonus, but rather apply the bonus regardless of which bionic limb they are using. So I guess that answers my own question.
2) I doubt it. Just a Standard Attack, if I'm reading it right.
It says: The character can strike with it as his Reaction for the Round or use it to make a standard attack.
So I guess it can only be used to make standard attacks even in your own turn? So you can't use it to all out attack or anything like that. As for the reaction, it doesn't clarify but I assume it would use the same limitations. On the other hand it feels like the rules are written as if you were using it along side another weapon in your turn (to get an extra attack) despite not being able to perform two attack actions in any given turn. It doesn't seem to take into account that you might be using the mechadendrite as your only weapon for that turn and therefore doesn't go into details about which actions can be performed.
I do wish Fantasy Flight Clarified these things a bit more, it's the 5th iteration of the manipulator mechadendrite rules since dark heresy!
3) Any time you can use a Reaction; in other words, any time you could Dodge or Parry.
So how does Furious assault work? Do you only get the extra hit when you get attacked? There are a lot of reactions that fall outside of dodge and Parry trigger conditions. Some like Furious assault don't function unless you use them immediately after your turn has finish, arguably the reaction for Furious Assault is used during your turn (which goes against the rules for reactions)!
4) The Mechadendrite is plugged into your back. There's no muscle behind the swing; it's all the machine. Ergo, I'd say no SB.
My arm (or cybernetic arm for that matter) is plugged into my shoulder, this doesn't stop me from putting the whole of my body into a punch. In my experience the punch starts at the legs. Would be my argument to that. The mechadendrite is anchored to your body I'm sure the same concepts would apply.
"Generally, there are 5 components to punching power that must be present for a puncher to be considered truly powerful: lack of arm punching, proper weight shifting, stepping during a punch, pivoting with a punch, and using proper footwork.
This body connection requires the development of a strong core. The core is perhaps the most important element in a powerful punch, since it connects the powerhouse of the legs to the delivery system of the arms." - Wikepedia on Punching Power
As for a rules perspective and why the mechadendrite entry doesn't say +SB, I would assume it the same way melee weapon profiles don't say +SB. It's only in the "resolving the attack" section that it clarifies that all melee attacks add your SB.
6) I don't really see any issue with that, but I would suggest not using the Mechadendrite as a weapon for that. An average fella with a Sword will be doing 1d10+3 R instead of 1d10+2 I, and you can rather easily snag a Chainsword or some other such nice weapon.
You can't perform two actions with the attack subtype in the same turn and knock down counts as an attack. Using the mechadentrite to attack as a reaction gets around this. Also if you take into account SB the mechadentride becomes more potent that the sword, and it's hands free. Well that's the idea behind it anyway.