Something must be seriously wrong with your Xe this means, as most great mileage a 3l engine could give is 10kmpl.
Hissa noise is not normal but one can say it is common.
Since this is a 4x4 only 2 things have negative affect that is Body change and duplicate book. By 13.5 if you mean purchase price then I would regret to inform you that you bought it really really expensive.
Better avoid power windown conversation as it will keep getting problems due to old windown rails..