Resolved.

Today was Me vs. The Shirt, round 3.  This time I won - all that remains to be done is to cut the buttonholes and sew on the buttons.

But let me back up and take you through the whole painful process. 

After I posted yesterday, I decided to try the collar again.  I probably should have waited to read everyone's advice - thanks so much to those of you who offered it!  (Also to those who commiserated!) But I wanted to see if using the Sullivan's Spray Stabilizer would help.

Before I got started though, I got out his RTW linen shirt with a band collar, and I noticed that the collar on it was much narrower than what I was using from my pattern.  And that made sense, since it doesn't have to hold a collar.

The original collar I picked out next to the RTW collar.

So I redrafted my pattern piece to the dimensions of the RTW shirt.  I'd already cut my new collar band pieces, but it was no big deal to just trim them down.

On my first collar, the outer piece was stabilized with lightweight fusible.  We all know that didn't work.  One of the pieces of advice I'd read online said to interface with self fabric, so for Collar #2 I cut three pieces, using one as interfacing.  I also took my seam allowances down from 5/8" to 1/4" because the band was now so much narrower.

I sewed Collar #2 together and then stitched it to the neckline.  But because this was my second try, and I'd already trimmed the neckline seam allowance after the first try, it didn't go on very evenly.  I ended up unpicking some of the original stay stitching that was showing through.  I also had to do quite a bit of hand stitching at the center front because my seam allowance was popping out.  I got it to the point of looking OK, but not perfect; by that time it was getting dark so I decided to put it away and sleep on it until today before deciding whether or not to unpick the whole thing again.

This morning I took another look at it and I just couldn't live with how it looked.  It was so sloppy in the light of day that I didn't even have the heart to take a picture of it!  So out it all came again.

But before getting started on Collar #3, I took the time to listen to the podcast on sewing with linen that Lisa G. had recommended in the comments yesterday.  While it didn't address my particular problem, I did learn quite a few things.  Linda Lee stressed that it's really important to true up the grain in order for the fabric to hang right, and I'll admit that I noticed some skewing on my first two collars because they were off grain.  I thought I had gotten all my pieces on the grainline, but honestly this fabric is SO shifty.  So with my last leftover piece, I took the time to pull one thread and cut across the space left by it to get a truly straight edge - not easy, since the softly spun fibers break very easily once unwoven.

I felt that my second collar was still stiffer than I wanted - it was just too much contrast with the drape of the rest of the shirt - so this time I only cut two pieces.  I sprayed them with Sullivan's and once they were dry, I sewed the two pieces together and turned them. 

Since I'd picked out some of my stay stitching around the neckline after Collar #2, I stitched all the way around again.  And this time, to help me get my collar on straighter, I marked a line for myself to line up the collar edge.  I marked just shy of 1/4", since my seam allowances for the collar were 1/4".  You can just barely see the pink markings in this photo:

p.s. this photo shows the actual color of the fabric!

And just to be extra sure, I hand-basted the whole thing on before doing my actual stitching.  It still didn't come out absolutely perfect, but it's pretty close, and I didn't think this loosely woven fabric could stand having the stitches removed again.  So I went ahead and did my edgestitching.  Here's my final collar:

Still a tiny bit of waviness, but far better than the first one.

So here's what I learned for using this fabric:

1) Make sure the grain is absolutely stackenblochen!
2) Use spray stabilizer.
3) Press, don't iron!  I realized I tend to iron my seams rather than press them, and that really stretched this linen out of shape.   I had much better luck when I used downward pressure only.

Once the collar was resolved, finishing up the rest of the shirt was a piece of cake.  The remainder of the seams were French seams - necessary for a fray-prone fabric like this.  This was my first time using a French seam on a curved seam like a sleeve cap, and I'm not convinced it's the best finish.  There's a little bulkiness at the shoulder because the French seam can't be clipped around the curve like a normal one would be.

I put two rectangular pockets on the front, and the back has shoulder pleats coming off the yoke:

And here's a silly picture of the whole thing (mostly) - because it was spread out on the table, it looks like the body is enormous and the neck is teeny tiny, hehehehe!

And now that I've spent a half hour or so writing this, the Fray Check I used on the buttonholes should be dry, so I can cut those suckers open and sew on the buttons.  But maybe after dinner . . .