Typically there are no 'rules' in English. To native speakers there are simply things that sound OK and things that sound weird. Many of us never learn grammar to know 'the rules' if there were any. But yes, 'for what concerns' does sound strange, and would only be used in either very specific circumstances, or possibly old-fashioned speech. As a general introductory phrase, it would definitely be a good idea to avoid it. There are probably quite a few, which would be used in different contexts. 'As far as xxx is concerned....', 'In terms of'. Don't over-use introductory phrases though. To me, that is something that can easily sound as if you are trying too hard.