Yet another confusing PS4/account questionFollow

Hey all, I've been reading forums all morning and I'm still completely confused about how to return to the game.

Here's my situation. I speak Japanese and English and have an old Japanese PS3, a new Japanese PS4 and no PC. I am a PS4 n00b.

I have the UK ARR CE for PS3 (which is linked to my UK PSN account), and I have a mid-level character on there I fooled about with for a while. Ideally, I'd like to keep using this account but it's not the end of the world if I have to remake (I wasn't exactly at endgame level).

I also played the PS3 beta in Japanese, so I have a different Japanese FFXIV account linked to my JP PSN account. I don't mind paying for the game again and activating this if necessary, and I don't mind the inconvenience of having to 'import' future expansions etc. I'm used to that.

So, I decided to return to the game and I upgraded my (UK) PS3 version to PS4 last night. It only lets me log in with my UK account and only when I'm signed into UK PSN (I prefer JP PSN but this isn't a dealbreaker...). I haven't renewed it yet so I can't play, but in the client's login screen I have to use X for confirm and O for cancel, which drives me nuts. If I have to play the entire game this way I will not be able to tolerate it.

I am also downloading the trial version of ARR (JP edition) from PSN at the moment to see whether it fixes the X/O button problem. However, there's one big question I have: will I actually be able to log into it? If it will be linked to my JP beta FFXIV account, should I download it on a different PSN account instead or will that refuse to let me log in too on the basis that my FFXIV account is linked to a different (UK) PSN account? Is there a simple setting to fix the annoying X/O button switch they seem to have irrationally hardcoded into the client?

What I want is a FFXIV client on PS4, which can accept EN/JP text input and uses O for confirm, X for cancel, and - if possible - will let me log in with my existing UK account. How can I get this set up so that everything works the way I want it? I don't mind playing in either EN or JP interface languages and I know you can switch spoken language anyway, so it's more the logistics of the clients and accounts that's making my head spin.

Thank you so much for any advice!

From experience on the PS3, I could log in with an NA PSN account or an EU one. Problem I encountered as a Brit was that while I could use the US PSN (I only really did this to gain access to US Netflix before they closed that loophole) was that I couldn't use the US Store. It required me to register a credit/debit card with a US address. I'd imagine this will be much the same for the PS4. I have one but haven't tried to log in on my old US PSN ID.

Regarding the X/O issue, you can remap every key once you're in-game. I doubt you can config the keys in the character selection screen for example though, only keymapping of in-game commands.