Is the Kirchhoff's Current Law correct?
Hint 0: No your formula is not correct. The capacitor is not connected to the Vth node, so it won't be involved in the KCL equation for that node.

Hint 1: Anything in parallel with a voltage source has no effect on the rest of the circuit. 

Hint 2: The Thevenin voltage can be calculated from the voltage divider formula.