Well spot. Yes functionally I want to make that key being "go home" by default. But did not put Android circle as the device is supposed to load other OSes as well and I feel the "circle" will spoil the feel of integrity under other OSes. So I want to reveal this one when it's formally launched, and hopefully it can be re-mapped for different functions other than just go home.
Yes, to achieve ´ and ¨ you can use ' and " indeed. for example: ' = á " = ä ` = à ^ = â ~ = ã
I don’t know if it’s too late but I think an orthogonal layout (like the N900 keyboard) is more suitable for thumb typing. Staggered keys just don’t feel natural when you want to flick your thumb from one key to another. But then again. There is no other modern phone that sports a hardware keyboard.