I have now finished the red side of the coat to the same stage as the striped. I have a few photos from the construction that I think I missed on the striped side. The first photo shows the wrong side of the front with the princess seam press open.
I press seams open first, even when I am flat felling them, because it makes for a flatter finish. On a princess seam, there is extra fabric on the side front piece that has to be eased (blended) into the other front piece. That is one reason why I have trimmed the seam allowance on the main front piece and am using the seam allowance on the side front piece to fold over for the flat fell.
Here I have folded over a little bit of the seam allowance and am holding it down with my left hand (taking the picture with my right of course). I have a fair bit of fiddly work ahead, as I have to fold under this seam allowance at the same time as work in the folds and wrinkles and not get wrinkles on the right side when I am done sewing.
I am pleased with the way the finished seams look on the right side or outside of the coat, especially on this plain red side. It's hard to see in this photo, sorry.
I am still stewing about the buttonholes and reversibility of this coat. I went on the internet to look for anything related and only found stuff about what I already knew. I have a reversible coat that I didn't make and it uses loops and buttons on both sides. Because of the loops, when you button it up in either configuration, the buttons end up on the left side. I am thinking I will make buttonholes using a patch method shown in my couture sewing book (from the folks who bring you Threads publications) and just put up with having the buttons on the "wrong" side (the right hand side, the way men's stuff is buttoned). This will mean I have buttons sewed on top of buttons but I guess I can cope. I'm still stewing. Maybe I will make a couple of tote bags while I think about it.
However, next I will sew the two halves together a the neck edge with the collar and see how it hangs after that. I won't sew down the fronts because I want to leave my options open for loops or other fastenings.