1) How could you meaningfully prompt for values if you don't know what to prompt for?
2) For yes/no parameters, you could use a build rule of
%MACRO_NAME% is defined
(or is undefined)
Then you don't need to predefine the macro but can toggle the behavior by passing on the command line (even to an empty value).
3) Sounds like you want your own custom GUI front-end to the build process. See here for ways to do that (2nd paragraph):
http://www.visualbuild.com/Manual/promptsample.htm