Combine the balsamic vinegar, sugar, and salt in a sauce pot and simmer until dissolved. Pour over the kumquats and allow to come to room temperature. Chill.
Toast the fennel seeds in a dry pan and crush in a spice grinder or with a mortar and pestle. Combine with the lemon juice and whisk in the extra-virgin olive oil. Season with salt and pepper.
Combine the grapes, oranges, shaved fennel, fennel fronds, radishes, and herbs in a bowl. Season with salt and pepper.
Gently toss with ¼ cup of the vinaigrette and artfully arrange on plates, about 8 portions.
Garnish with kumquats and sprinkle with pistachios.