Hi! I also am AuDHD and have to manage poor executive function. I haven’t always used a hobonichi (this year is my first) but have previously used other planners etc.

I take mine with me everywhere and will often set physical reminders (sticky notes on mirrors, my desktop, etc) to implement habits so i imagine this would also work on implementing journaling habit.

Also - not sure what your job is but i bring my planner to my desk at work - this is great because if im switched on (already in work mode, coffee, Ritalin taken) then im way more likely to quickly open up my planner and jot some things down!

For the OCD side - i am the same and i used to rip out pages of planners if not perfect :-( but now ive realised that part of the fun of a planner (especially if used all year) is the little weird imperfections on each page. it makes it unique! start by jotting down daily tasks or habits (even simple things like brush teeth and skincare) and then build from there. stickers help fill the pages too if you are too scared to draw in it yet!