Danger from NOT connecting cables
"Until an electrician installes everyhing correctly it might take some days or weeks - is it okay to have all cables loose and unconnected (with the ends protected against touching, off course) in the meantime?"

"Or is there any danger from NOT connecting cables?"

At least one of the four wires you describe will be "live" and (literally) have the potential cause injury or death through shock and/or fire. Please make sure that you do indeed insulate each end away from others and anything conductive that may come into the box. Otherwise, as long as the wires are as you describe, they should be electrically safe until the electrician gets there.

One thing, not safety related, household fixture LED's usually come as "dimmable" and "non-dimmable. You may want to double check to make sure this is a dimmable LED, as they use a duty cycle to quickly flash short or long durations to give the appearance of dim or bright light.