Lots of good advice here, but to follow some of it you might feel more confident with a helping hand. I think you could hope to find a Fairphone Angel in the vicinity.
I would certainly follow the advice about moving your photos and videos to a SD card (as Urs says, formatted as external / portable memory). You only have 6Gb or so free and some apps may feel a bit short of space! The following article may be of help.
Your phone may be needing a cleaning of internal contacts. Here again a FPA might assist you.