I finished the toile of mine last night, and it looks like all I need to do is shorten the sleeves, bring the hem up a bit (so the longest part falls just below my knee instead of almost at my ankles) and take some width out of the waist (so it doesn't paper-bag when belted).
I'm thinking then that I might take a look at the Simplicity 8262 pattern and see if it gives me an idea of what to do with a buttoning front for a coat.
It's still frustrating though, and I still really feel like I need to look at another jacket or coat pattern to make sure that I actually have it right.
And there's so much more sewing I want to get finished, but so very little time... I think some public holiday weekends are coming up though, so I might have a chance to put enough time in to something for once.
Essentially, what I wanted was an underlap a bit narrower than what you might do for a double-breasted coat (but enough to improve the rainproofing over a standard button front) and the overlap such that the buttons sit on the CF line. I know, that probably means cutting seperate left and right fronts, but oh well.
I also just realised it would be worth doing a two-piece sleeve since the fabric (cotton canvas) is stiff enough even before waterproofing, and I doubt it softens up much.