Board Thread:General Discussion/@comment-18053181-20141214100556/@comment-6697950-20150217060016

Whether or not you read the Progressive series will not affect your reading of the main series. It is an interesting read, but it's all up to you if you want to read it. The first volume in English will be published at the end of March. As for your last question, the first volume in Japanese was published in 2012.