All done
After all my fretting about how shrunken the sweater looked as I was knitting, and whether I had miscalculated the fit, everything relaxed in the wash as planned, and the fit is perfect, just the right amount of ease when buttoned. And the fabric drapes beautifully — so glad I sought out a longwool yarn. 
I think the back is my favorite part of the sweater — I wish the front had more of this look, but once I committed to reversible lapels, my options for the center panel were limited.
The collar can be buttoned up to the neck on chilly days.
Blocking
This washed beautifully. I’m doing minimalist blocking — no pins, just a laying it out and verifying that the measurements are still as expected. All those lumps and bumps I. The sleeves from multiple re-knittings disappeared like magic.
Button choices
with first button band on, it’s time to review the button choices. The larger mother of pearl and coconut shell buttons I thought I would like based on swatching look a bit large on the finished band, so the smaller smokey shell buttons look to be the best choice.
With my button choice finalized, it’s on to the second button band, and buttonholes.
Collar, revised
I ripped out the collar and neckband, picked up fewer stitches along the saddles and back neck, and reknit a narrower collar — narrower by almost the width of the button bands to be added.
I will have to give up on the option to wear the collar buttoned up all the way and loosely folded over, but I’m much more likely to wear the collar open, and it will look more balanced this way. Picking up fewer stitches also gives a closer fit around the neck and I the necline did not pucker as I had feared.
The collar
I really like the way the collar looks … now. But once I put the button bands on, it will be 1.75 to 2″ wider on each side, and hang down over the shoulder( and I can’t leave the button bands off, or it won’t close).
I could re-knit the collar, and pick up fewer stitches across the saddles and back neck, but not 4″ worth, without leaving puckers. Decisions.
Construction notes: double needle pickup across the saddles and back neck, to a height of 1″ across the back neck, tapered with short rows along the saddles to 0.25″ where the saddles meet the front. Fronts then knit from live stitches connecting along the saddles with short rows to the level of the back neck, where the rest of the stitches were picked up and knit across.
Pockets (or not)
I’ve been back and forth worrying how to construct the planned side-entry pockets without breaking the line of the front pattern or interrupting the fabric drape with the bulk of additional layers. I was planning to get matching fingering weight and leave the inner pockets hanging free, but they need to be above the line of the side vents or they might fold back and show in the vent opening if they were set too low. If the pocket opening was set too close the the vent, the fronts might be unstable and stretch oddly, given the relative thinness of the fabric.
I knit up ~3 inches above the side vent join, ready to start the pocket opening, and realized it would be set awkwardly high. Given the planned length of the sweater and the length of my arms, the side vents and side-entry pockets just don’t work together. The side entry pockets were perfect for my old favorite sweater given the coat length and and full side seam, but the proportions are different for the sweater I am knitting.
I’m happy with the vent detail and slightly dropped tail — the side entry pockets will, reluctantly, have to go. I still have the option of a standard top-entry afterthought pocket, which would definitely break up the line of the front cables, or I’m considering a hidden inner patch pocket. Or maybe no pockets — I think about it as I continue kbutting the fronts.