The best way to get any info on a Tadao is to email them directly, Will at Tadao is usually very quick to return emails. I don't have any boards handy to make comparisons on for you. To my knowledge, E1/ZeroB boards are not the same size as E2's; the LCD screens are slightly different sizes I believe. I'm not sure how the Yakuza OLED screen compares. I would assume it is closest to the E2. Hopefully, someone on here can confirm some of this.
As for the FBM frame, I assume you've seen DOAT's Merlin? He got a Yakuza into his FBM frame, you might ask him for more info on how he exposed the screen.
He would probably also be the one to ask about the board modifications. I believe he modified his Yakuza to accept a microswitch instead of the optical switch. I think he also modified it so that the buttons were relocated to the side in one of the grips, rather then the back of the frame.
You might find that the FBM modifications are easier then the UL ones. I think Blackbean managed to put an Eblade board in a UL, but he had to mill out ALOT of material.