1) I was wondering how to reduce the heigt of the slider if possible. – Slider height is auto adjustable according to image height. You can add the image has less height and slider will adjust.
2) Also I was wondering if it is possible to deactivate the slider on the homepage itself. Reason is that te slider takes a lot of place and I would like the viewer to see the text instead of the whole slider. – Yes, Please send us the site URL so we can send you the code.
3) Is it also possible to change the layout so that the text comes first and below eventually the slider? – It can be possible but for this we need to make lots of customization in theme files. Since it’s customization part and can be chargeable.