The lashings are used rather than adjusters because they are lighter, cheaper, probably stiffer, stronger and have a better resolution. They are not repeatable, but that's ok because the lowers can live on the boat - you put them into the mast when you put the mast up. The 4mm resolution you get with a chainplate is not good enough. I know this because I made the very same mistake you are contemplating on LFC in circa 1996. Be a smartiepants and save the £17.28!
http://shop.pinbax.com/index.asp?selection=detailed&uid=12217&itemtitle=Vernier%20AdjusterStruts protect the mast from gybe-related breakage. Many broken masts testify to its importance. Ross probably has the mast fitting you need. We have at least two carbon struts you can have, and probably the mast fitting too.
A self tacker looks groovy and speeds up the gybes, but it is heavy, expensive, difficult to set up, and on a small rig boat with no snout, you will pay a sail-area penalty. It also reduces one of the many really special things about Flat Stanley: Go sailing in anything, anywhere, and be having the time of your life. The reason for this is that a self tacker cannot let the jib flog straight out like a flag. After a big stack in big winds you don't want any obstacle to getting back upright again. A self tacker is such an obstacle. Also: What is the purpose of a self tacker? It's to allow the crew to take the mainsheet through the tacks. On FS the helm is not trapezing so will have the main - so no need for self tacker.
Very well done on the foils. Here's a GPS track of Ross and me in FS on KGSC, with the foils all furry:
http://www.sailingsource.com/cherub/GPSAR/gpsar.php?filename=KGSC-20080126a.gpx&maps=maps/kgsc.mapsWe top out at 17.2knots or so. You will get more at Netley!