I decided to settle for a solution that would also take care of my other problem, namely how to wear a round shawl. Do you fold it over, or scrunch it up in your neck? And wouldn't it make sense to have just the part of the circle that you can actually see? In a blanket it makes more sense, but I've always wondered how you'd wear a round shawl. So I knitted a wide wedge, with six tenths of the pattern repeats.
This meant knitting back and forth, instead of in the round, and some of the patterns ended up having pattern rows on the wrong side, too, but nothing too challenging so that didn't turn out to be a problem. Most of the time every other row is just plain knitting. I also had to figure out what to do with the edges -both edge stitches, and the shape of the edge for when the pattern wasn't straight. I used two garter stitch edge stitches, which is pretty typical of lace shawls/scarves. The leaf pattern I knitted out so that the total stitch count increased in the first part of the leaf and then decreased for the second part. The diagonal rows of holes I cut off so that I got a straight line for the edge.
Otherwise I had no problem knitting just six tenths of the pattern, and the patterns and stitch counts all behaved very well and caused me no issues.
The needle size for lace depends on the amount of empty space that is desired and how airy the resulting fabric should be. My yarn was buttery soft, quite substantial and heavy, and I didn't think it could necessarily hold up to a very "lacy" or airy structure. Plus I wanted the shawl to be quite substantial, as well, so I used a 4 mm needle. If I had just gone based on the ratio of my yarn weight and what was recommended for the yarn weights in the pattern (4 mm was recommended for the fingering weight and 6 mm for aran), I should probably have used at least 5 mm needles. The 4 mm needles produced, however, very good results, and the size, I think, is pretty perfect!