You do not have to use a 64 bit version if you're using a 64 bit OS, the 32 bit version will work just as well (except for access to the 64 bit memory address space).

The 64 bit version is no faster, that's not what 64 bit programs mean. What it does mean is that it has access to the full memory address space that 32 bit programs do not have access to, which means that Windows will allow the program to use more memory to complete memory intensive operations (such as exporting exceptionally large websites) that are limited to around 3.5GB for 32 bit programs.

Yes you can still use Ctrl + Shift + Alt + S to switch the UI to the light grey interface.

You do not need to export your website any longer when publishing from Designer, the publish operation has been streamlined so it just publishes the document without needing to ask you where to export first.