RAM and Cache issues despite enough disk space

So, i turned out that communication with an external SSD caused major problems. Re-formatting that one helped for the most pressing trouble as did working completely inside the macbook pro, but that's not a long-term solution.

Anyway, while things got better, they did not disappear.

I do still run into out-of-memory trouble when the assigned space is used up (but now only then, which is improvement) and neither purging Disk & Memory Cache via the menu nor Empty Disk Cache and Clean Database via Preferences does help with that one.

I need to restart AE to make previews work again.

That's better than having to restart the whole machine but it is still annoying. If any solution comes up for this one, i'm highly interested.

Yes, i did lower the cache size and it did not help.

Currently i am testing something else and i'll post here if it turns out that that was the problem. Give me a day or two to test thoroughly. And thanks for the suggestions so far.

If you change your Disk Cache preference to be 400MB, does that make the error go away? Because we can't always know how the block size on a drive, there is a bit of slop built into the AE warning so we can account for the variation as disk space is filled up. Assume if you put 500MB, that AE is checking for more like ~550MB available, which is right around what the OS is saying is available. 

Thanks for your reply.

I'm working in AE since version 3.1 and up to Intel i had a fairly good knowledge of how ram and cache and disk space work and how to set up my compositions in order to get the max out of it. I did play around with everything i know already, thanks for your suggestions anyway.

Silicon and their unified memory and AFPS seem to be a different planet but Adobe claims to be Silcon ready, so i was hoping they have some ideas somehow.

Hi!
First off, I don't think you have plenty of space for a 500GB disk cache. Unfortunately macOS isn't always straight in how much space you actually have left on your disk, as the system and other programs also uses disk cache and not always shows how much those take away from your availability space. Just check your screenshots: finder says 730GB, Disk utility says 558GB free. 730GB can be free (if some files are uploaded to iCloud and caches are cleared for example), but only 558GB is probably actually free. Usually I would advise to always have at least 500GB free on the system disk. I would try to first change the disk cache to about 200GB or 250GB instead of 500GB and see if the warning disappear or come later.
But then, I'm not sure this is the whole root of your problems as previews are usually run from the RAM, not the disk cache, and your screenshot shows the disk cache only contains about 30GB, which should not be a problem with 500GB free disk space.
Also 16GB of RAM is not that much for high resolution, high bit-depth previews, that will fill up fast even with relative simple comps. Lowering playback resolution and bit-depth will give you some more preview length, but that might not be workable for your specific project. For working with high resolution, high bit-depth material and comp size the only solution is more RAM but unfortunately you can't add RAM afterwards on your system...

So I don't have a clear solution but maybe playing around with the Memory and Performance settings and see if that will help a bit?