I put Lazy Jacks on my boat two years ago and I love them.
I designed a four part Lazy jacks system for a boom almost 16 feet long. The attachment points on the mast should have been placed so that the lazy jack would hold the end of your baton as the sail is furled. I didn't consider this and attached my lazy jacks just beyond the end of the baton (I have a full batoned main), allowing the end of the baton to fall off the boom. I'll fix that in the spring.
One thing I did right was to use a control line. My Lazy jacks are attched to the mast just below the lower spreader. I've never found a majic formula for determining where the lazy jacks are attached to the mast, but I'd suggest 1.5 to 2 times the boom length above the goose neck. At that point I mounted a Harken #233 Micro Block on the mast and ran the control line back to the goose neck with enought slack to allow the lazy jacks to be hauled down. A major complaint with Lazy Jacks is getting the baton caught on the lazy jacks as the main goes up. I can release the control line and gather the lazy jacks up to the control line cleat near the goose neck before I run the sail up. You'lll want this feature!
This cleat also secures the control line. Many plans show this mounted on the mast. Don't do it! Instead, mount it on the boom 12 to 18 inches from the mast. This keeps the control line away from the mast so it won't slapping at anchor.
It's a great DIY project and worth the effort. Good luck.