Yes, Yes and NO. If say purchase price is 30k, it would normaly be $1,800 of gst to be paid, with trade in, net purchase price is reduced to 15K, gst to be paid is $900 (at this point you have technically got your full credit on gst from trade in). Your lease payments are based on the net Purchase price less residual plus financing, then taxes are calucated on that monthly value.