I’s been my experience that when setting out to design a custom PCB on a new chip it pays to have some known board to debug off of. This can be useful even if there’s no relevant peripherals on there. Either add them, or simulate them, or maybe even double check that that pin actually is tristated when it’s supposed to!
Specifications I know. I usually get them from other people. At least I did. Just like those sentences, I can with this project – do whatever seems appropriate. Like ugly long sentences, that are hard to read because I make you look for that period until you mind is figuratively (and even make unnecessary asides just to let you know that “literally” would be entirely wrong in this context; and you already knew that) exhausted.