I finished the shirt!
I'm really pleased with how it turned out. I originally bought the Simplicity pattern for a basic men's shirt, but the pattern didn't look as simple as the brand name might imply, so I scouted around for an alternative, and settled on the KwikSew one, which I was really pleased with - the pattern was coloured, on thicker paper than the superlight stuff Simplicity use, and the pattern was easy to follow, and allowed you to choose a custom neck size no matter the size of the shirt.
He looks great in it, and I'm glad I took a bit more time to topstitch the sleeve and side seams. I've included a few photos of the detailing, just to show off. I also converted the basic cuffs to French cuffs, because he's starting to accumulate quite a nice cufflink collection, and I love the look of them.
The fabric is plain black poplin with metallic silver skellies on. I figured if I was going to do my first test run in cheap poplin, it might as well be cute cheap poplin. :) As it was, there were no major errors, mishaps or unpicking, so I could have gone straight to the posh stuff, but I think it was nice to just go for it without worrying.