Since he is often busy with work and gets a lot of e-mail, it can take a while to respond. Don't worry, someone will almost definitely get back to you. The latest version is 3.0.8b2 as of this writing. Development is beginning on htdig4 as well as an interim release of htdig3. Not at the moment.
Binary distributions are on the TODO list.
Currently no other mirrors exist. Not at the moment. You then create a configuration file that specifies which files to use. In the html document that links to the search, you specify which configuration file to use. Default You would also put into the configuration file any other lines from the default configuration file that apply to htsearch.