As I have said earlier, to claim that V3 = V4 is incorrect. Read my earlier post.
Well yes, that is right. But you do know that the above expression gives only 1 nodal equation, that is, the nodal equation for node 3. You would have to do the same thing for the other 3 nodes.
This is not right- you're forgetting V3.
These are correct.
And yes, combine these terms into an equation. Note that Vb = V2. Also, at the moment, let's forget about V2 = V4-2. Now write down again the nodal equation for node 3.