Yes, correct, it will give you 4cm lift. You should adjust the LSPV ..... you are changing the extension distance of the suspension. 4cm is not a big difference, and won't affect the adjustment too much, but it is better to compensate.
The steering should still be fine, and so should the front prop-shaft. However, if you have already done a suspension lift by changing the springs, the overall lift would be compounded and you would probably have to lengthen the prop-shaft, drag-link and brake lines. You would also have to lengthen the torque rod on the front axle if your vehicle is fitted with one. If your overall lift from standard ride height is 100mm or less, none of the above should be necessary, but check the brake lines under full extension to ensure that they are still long enough.
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