4.2.- Can I adjust air pressure before installing the element in the fork?

It must not be done in any case!
As indicated in manual, air spring is to be installed right after the helicoidal spring, without any pressure in it. On top of it, if you notice that when installing the air spring it remains slightly high with respect to the bar, you should release air by pressing the valve and then push to bolt the element.
Installation should be softly made to prevent damage in the threads.