PeterH:
What operating system are you using on the PC side? These features all seem like things that could be achieved within the PC without needing any custom keyboard hardware.
I will connect the keyboard not to a real PC, but to different hardware, which have USB keyboard support but have typically no possibility to change the layout and if possibility is there (which is rare), than it have definitly no support for Dvorak/Colemak and similar. And I want to use the keyboard, which is already there and do not want to take a modified keyboard with me, but only a small adapter. They are already some keyboards which do what i want pretty well, for example http://tinyurl.com/p23h7hr but again, I do not want to take the big and havy keyboard with me every time and this keyboard is to expensive to by 10 of them.