ProGuard has nothing to do with the API level of your application. Newer versions of Eclipse ADT are integrated, so to use the addition of a separate line in the configuration file, you do not need to use Ant. You may have problems if ProGurad removes the methods / classes that you are actually using, and you have to work around them by setting up the ProGurad configuration file.
If you find it difficult to use, you can always run the application without obfuscating it and add ProGuard to a later version. If this is your first application, the likelihood that someone will decompile it to steal your top-secret code is pretty low :)
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