Thank you all for the comments over the last couple of days. Your sound counsel has kept me going with my Negroni. I have heeded your advice, and my gut instinct, and ploughed on with what is, and even from the outset was intended to be, a practice piece.
Since my last post I have attached the sleeves to the shirt with a flat felled seam as per the directions. This didn't go too badly. Nice clear directions that really work.
The sleeves went in quite well. The sleeve cap of the first was a little longer than the armscye (maybe 3/4"?) but the second was very nearly an exact match.
This is not my best work (I have lost my parallel on this top stitching) but as I look again at the pictures it's really not that bad either.
I have sewn up the side seams. This picture is taken from the inside of the shirt (note the outline of one of the pockets). I went to a bit of bother to try and get these right. There is a slight tuck where the side seam crosses the armscye seam. That point was the tricky bit. The difficulty I experienced there made me want to examine the ready to wear shirt I was wearing more closely. The seam I found under the arm of my factory made shirt made me feel better about my own work.
Next up were the sleeve hems. Back on familiar territory and back on song with my stitching. Both sleeves are the same length and the same width!
Last up was forming the hem at the bottom of the shirt: turn 1/4", turn again 3/8" and edge stitch from the inside.
So - five button holes tomorrow evening will see my first shirt completed. I think I'll probably make these on the 401K but I might try out some samples with the buttonholer rigged up on the 201K. It would be nice to say that the finished shirt was 100% treaddled after all.