UHD BD’s can be 50 to over 100 GBs in capacity. Also can be triple or quadruple layer discs.
Looking at my uncompressed mkv rip of Independence Day 4K, it’s at 42.4 GB.
Bitrates can be nearly 100mpbs. Editing 4K videos takes a lot of power. If I have to edit in 4K I use a mix of NLEs like Davinci and After Effects.
As far as authoring 4K Blu-ray at the moment, well you better be rich. There is no consumer level software available. There is a tsmuxing variant (I can’t remember the name) that is attempting this but has severe limitations as it only works with BD50 discs and does not retain HDR metadata and can only mux streams and no menus and it’s also at a bitrate of around 30mpbs.
It’s still early on in UHD BD’s life.
As far as rig specs go for editing, yeah you’ll want at minimum 8 cores and 32GB of RAM as well as at least an NVidia GTX 1060 to help edit.