Atasan,
Very impressive work so far.
Supporting this blade, which has an appreciable mass, requires a combined truss support. You have shown truss structure in two arms (which is good) but you will also need a cross-brace between the two arms. I recommend attaching the cross-brace from the bottom of the wing to the top of the hub. This will put the cross-brace in tension. That will be more effective than having a cross-brace in compression, because if it buckles slightly, it could collapse completely if it's under compression. Spreading the hub attachments of the two arms will also increase the stiffness of the whole system immensely.
Make sure to compute the radial forces on the hub before selecting a material for the arms.
I built a VAWT many years ago - 2 meter blades and 2 meter diameter. Its speed was limited by vibration. It had many modes of vibration, too. The fatal one was what I would call "whirl", where the top of the mast traces a big circle in the sky. I gave up when my attempts to correct the whirl imbalance caused more blade pitch imbalance.