Very, very simple. Make a journal entry the first time on entering Arx, suggest that we visit Kemm, put a marker on him.
Afterwards, update the entry so that it suggests we look into various things 'We should probably investigate where the White Magisters have gone, I have a feeling that we should start our search in the Barracks to look for clues'. The White Magister's area for the most part, gives you information on ALL the other quests and areas, it gets you started in them at least. I literally did not find it on my own, I beat the game and restarted a save just before the end, and searched around for hours fruitlessly. Eventually someone suggested that there was a hidden Magister area on the forums, so I investigated and found it.
I didn't like Arx, wasn't much to do, and I was perpetually fumbling in the dark to figure out what I needed to do. With the Reaper's Coast we found the important person literally on the main road, and then they put us on the path. After there it opened up, but we still had the general idea of what we were looking for, and how to progress. There were plenty of secrets to be had, though none were frustrating for me to find.
Arx on the other hand...definitely could have used some elucidating. I do like the idea, though not the execution with a lot of the hidden secrets in Arx.
A journal update alone would definitely solve quite a few of those issues, giving us a general direction.
"Rumors have it that there is a hidden White Magister base somewhere around the barracks, we should look into this."
Since everything else pretty much ties in from that base (secrets there reveal such things), it only makes sense that an attempt to make it a bit clearer would be made.
I've put in 120 hours into Divinity Original Sin 2, most of them after release, so I'd say it's a safe bet that these tips would be much appreciated.
If anyone knows, what are the Kemm's Wedding Rings used for? In game it claims that they are shaped like a Key, but I've searched high and low, and found nothing that they'd be used for. Unless it was a chest or something I lockpicked.