1) You might be used to having the cancel button down there, however that's just a personal preference. Have a look at the screen when you try to delete a world; the cancel button is at a similar place as to where we put it in the login screen. Where would we put the register text if we were to swap those two buttons?
2) Unless you have any suggestions, the only option is making the buttons as big as they are in the minecraft options screen, however that'd cause all the buttons to go offscreen, I don't think we want scrolling in that screen either.
3) You can change all of your keybindings by clicking on Options...
-> Controls...
4) I assume you mean 'pasting a command in a commandblock': Works for me and I don't see any reason why I shouldn't with the mod installed. Try to uninstall the mod and check whether it works with just forge installed (sounds more like something potentially caused by forge).
5) Here you go. I don't think the amount of users wanting to track their ingame time is even close to large enough to justify adding an extra ingame timer. Nor do I see anything wrong with using an external timer if you wish to time your sessions.