I strongly recommend knitting up neck and front borders before starting sleeves when knitting sweaters. You'll get a much better fit at the point when you can try on the sweater to judge sleeve length. While surplice-style borders seem straightforward, they are in fact rather tricky to design if you are intent on getting a good fit (apparently, a lot of sewing and knitwear designers lack this intent, at least from my experience). This border style requires some finessing around the neck and shoulders to avoid unsightly gaps. See this post.
That said, I finished up the neck and front border on my new Wheatsheaves this morning. It took two attempts to get just the right degree of tension in the bind off. Here are some hints:
1. DON'T use a stretchy bind off such as Jeny's Surprisingly Stretchy Bind Off. The border edge will be ruffled instead of flat.
2. DON'T use a larger needle to bind off. The edge won't be ruffly, but it will still end up drooping over time.
3. DO use the same size needle as you used for the rest of the border.
4. DO consider using a dpn of the above size in your right hand when binding off, for ease of movement in working the edge.
5. DO make sure to work the last 2 stitches together as you finish to make a beautiful, tidy corner. This is a great trick to ending a lot of pieces with a sharp 90 degree corner.
6. DO lay the work flat to see how the borders are lying, and,
7. DO make sure to try on the cardigan to test the tension around your neck. Take note of how the extra width in this cardigan shape means that the sleeves will join the body low on the arms. It's intentional. If you're worried about your yardage, you might feel better knowing that the sleeve lengths are proportionally shorter than normal because of this.
8. DO be prepared to pull out the bind off row and do it all again if you're not satisfied. You can wait if you like and see how the whole thing blocks. Just remember that if you decide to re-do it, you'll need to steam the unravelled wool to get out the kinks for a smooth second bind off attempt. Get it right. It's worth it!
