you can you this as a reference https://wiki.archlinux.org/title/Localization/Simplified_Chinese#Chinese_characters_displayed_as_variant_(Japanese)_glyphs . although it is for chinese, but you can take the font config of it and reorder it (put Noto Sans CJK JP at first)

yes you can. but not for recent released tablets. you can find more on devices page of pmos wiki

android tablet have many way to run a linux user land . but most of them are still using downstream android kernel. which means you wont get any 3d acceleration in your “linux” environment. so i would suggest you some sbc based tablet or some chromebook (then install linux on it manually)