Glad jeans aren't a priority. JC and BR work fine for me.
I think the dark shirt is a bit too dark to go with jacket and tie. Though dark denimish shirts seem to be sort of trending (and can look good. @EFV comes to mind).
I have one double breasted. Solid navy F/W. I wouldn't mind owning a nice solid brown DB, though there are a few other pieces I'd probably want first.
I doubt I'd go beyond two DB's. I'm just not (psychologically) comfortable in them.
I don't own any gunclubs, but I have a light colored brown houndstooth suit that I struggle with squares for the same reason. I think I will (have only worn it once), going forward, stick to either white or something mostly solid.