You start off with what I'd call an excellent list, except that I can't get tarragon to grow for me.
Lemon balm. Good tea for ladycramps, feeling generally bleah, mild general anxiety, light to moderate fever, and cold sores. Great to lure bees. Grows low (shin-high) and tidy, good for the front row. Perennial.
Cayenne for all kinds of problems. A cayenne pepper in a pot can be lifted every fall and kept alive indoors. Plant it up front, because it is much more refined-looking than most herbs and because you want to pick it over every day in the late summer.
Pennyroyal, unless you grow it in hanging baskets like I do. It creeps, and it really does help with the fleas. It also makes a good headache tea. In quantity, it can cause miscarriage.
My other ideas all would require rather more room than you have:
Turmeric, to fight infections, gingivitis, etc. (If you have real winters, you'd have to lift it every fall.)
Valerian for the back edge of the plot. Beware--it stinks and draws both cats and snails. It also grows as tall as me, although not as wide. Dig the roots in the fall, chop roughly, and run them through the dehydrator. Use the runners for your new plants.
Ginger, another tender root, for stomach troubles and coughs. It looks a little like bamboo without stalks. Mine doesn't flower.
Milk thistle, for the liver and gall bladder. It's slow to germinate, and prefers dappled shade in Florida. The seeds are the safest part to eat, and since I have bad luck with milky-sapped plants, the seeds are the only part I'll deal with. A good plant will about three dozen flowers will yield a handful of seed. Not for nursing mothers or lactating animals. It's a thistle, all stickery, so you'd plant it in the back, next to the valerian.