little things...

I know you’ve got a ton of questions! Like, cutting that armhole in farther – do you make a longer band? No, I don’t. I like the way the 60-0-60 st band fits and it may seem a little more gathered as you’re doing it but you can’t tell once it’s on the finished garment, or on you - just do the same thing, keep the gathered part more to the ends/underarm section and it’ll all come out in the wash!
Oh yeah, about making that armhole band (and the neckband for that matter) the original pattern says:

right end stitch easier to pick up

Stockinette bands. Cast on with WY, 1 row ravel cord. RC000. MC, T5, K6R. T8, K1R. T5, K6R. Hang hem by picking up first row of MC. T7, K1R. Remove on WY or garter bar.
What I really do to make it work a little smoother (she said, after the third set of bands) is this:
Stockinette bands. Cast on with WY, 1 row ravel cord, ending CAL (carriage at left). RC000. MC, T7, K1R, T6, K1R. T5, K4R. T8, K1R. T5, K6R. (that initial looser row is the one to rehang and the bigger stitch size makes it easier and doesn’t show of course. The T6 row was just the transition to the next T5 row. You still have 6 rows on this side of the folding row but that side ends up as the outside of the band and having the outside slightly larger makes it fold nicer and lay flatter.) Hang hem by picking up first row of MC (easy, peasy because of the larger stitch size. T9, K1R. (That makes it easier to pull off on the garter bar and it also gives a bigger stitch that is closing the hem AND doing the join later to the garment edge!) Without cutting MC, remove on WY or garter bar and set aside.

whole stitch at left end

The CAL at the beginning means two things – when hanging the hem, that little impossible half-non-stitch usually at the left is much easier to find when it’s on the right end and you’ll have up with a whole stitch at the left and really feel good about yourself! Secondly, after hanging the garment, you turn the band and rehang to join it to the garment. The cast- off row will now be right to left, much easier to chain off in that direction and less ends to darn in. You’re welcome!
For the band on the vee side, I used the mitring technique from The Neck’s Best Thing, No 3, Mitred Stockinette Band, making it just for that piece, putting the mitre in the centre of a 50-0-49 stitch band.