1. Some people mentioned that this would "only affect RAR files" and it would be safe to extract 7z files with 7-Zip prior to version 18.05. This is wrong, because 7-Zip detects the file type from the magic numbers at the beginning of the file. So the exploit can be renamed to 'exploit.7z' and it works just as well.
On /r/sysadmin, someone even mentioned that a temporary solution might be to block RAR files. By the same argument, this is unlikely to be effective.
2. Almost all versions prior to 18.05 are affected. I manually checked version 15.05 and 17.01, and they are definitely affected.
3. Not only 7-Zip itself is affected, but essentially all software that uses 7z.dll as library to extract files. This includes various anti-virus software. However, exploitation may be more difficult (though not impossible) if ASLR&DEP is properly enabled (on all modules).