To make applications use Kmail instead of Evolution when handling mailto: links and etc., go to
System -> Preferences -> Preferred Applications and change the Mail Reader setting to Kmail.
I doubt some of the other changes you are asking about are possible.
I am not sure, what consequences it has to remove evolution as a package (since it is quite integrated in ubuntu-desktop), however, you can additionally install Kontact.
You could also just install kubuntu-desktop, which brings you the whole KDE desktop on (K)ubuntu. You can then decide during login if you want to use the Gnome desktop or the KDE desktop.
If you would like to sync between an existing data set then you might like to try opensync as a transfer medium.
The indicator calendar is getting massive attention for the Natty cycle, so it's likely it'll have strong bindings and all it requires is a kde developer to tie akonadi to it.
The open office integration is a simple code change, but it isn't simple to implement.
Over all it would be easier to wait for the dbus work in evolution to complete so your Kontact client data is simply the same backend that evolution uses and thus that evolution is giving everyone else.
