You would be better talking to Skylum about Luminars incompatibility with Affinity Photo or Affinity/serif would be better liaising with Skylum to find a solution if one can be found. but I'd say it's just not possible to get luminar to work without some code changes to luminar.
3. The caching of these files needs some serious enhancements! Luminar stores these preview caches on a Mac in the following folder: User/Library/Application Support/com.macphun.luminar3. And with each file you look at in the super large view, a cached version is created in that folder that is roughly some 15-20% bigger than your original file! So I have a 43MB RAW file and when I preview it in the Library, I lose 51.7MB of hard drive space on my computer!
Same here, i tried a lot of them and ended up still using ps still with luminar and aurora as plug in. I always try to use capture one, especially when i use my fuji ... but in the end i return to PS.
In the end PS with panels and plug ins amd actions make for a very powerful albeit expensive tool.