Plant KVAR = KVA - KW = 4500 - 2700 = 1800KVAR
First of all, you don't subtract kw from kva to get kvar's. It is a trig function, not an algebraic one. Use the pythagorian theorem to get 3600 kvars, or since .6 is the cosine of the phase angle, find the sine for that same angle and multiply it times the kva.
"If we provide the same amount of KVARs leading as KVARs lagging then don't we correct the PF to unity?"
True. Quite frankly, I got lost in your math. I suspect you have included more formulas than you need. For one, as long as you are dealing in kw, kva, kvar, and Hp (as equaling 746 watts) I don't think you need to incorporate the square root of three (1.73) at all.
Beyond that, I am totally lost.