Hiya RiK, I wish I could help but I know next to nothing on 4K writers and which brands / models are worth getting etc. Sorry man.
railerswim has a quality UHD Blu-ray Authoring - Technical Discussion thread. It seems, going on that… there are software shortfalls and limitations that many of us may be unaware of.
It does seems easier to store our content on external hard drives and have Plex / kodi / media centre style setups - than work on making 4K discs and the like (plus given the cost of the 4K blank discs themselves… making coasters could be a costly exercise 😉)
I hope to be proved wrong on the above and a few people chip in some actual useful advice and info 😃