I’m probably the worst one to ask because I gear everything around my individual bunnies’ needs.
My two girls are a bit sensitive to foods high in calcium so I limit those foods and try to stick with ones that have a diuretic effect. Kieko gets no kale, Marlee gets a few bites occasionally. Moshi has no calcium issues but has a sensitive tummy. He loves kale but still only gets a few bites when I buy it. Parsley is high in oxilates (flat parsley less than curly) and Moshi can tolerate a little so all three of mine may get two or three leaf clusters depending on the size. The base of their salad is green leaf lettuce, with red leaf mixed in. They may also get a little dandelion greens, basil, mint, or dill. Kieko occasionally also gets thyme or marjorum, and romaine lettuce. To keep all tummies happy, I have to stick with mostly green and red leaf with the other things added sparingly.
I think the rule of thumb is 2 cups of salad per 6 lbs of bunny, so 1 cup for a three lb bunny. I believe you could vary that based on how well your bunny handles greens. I’ve also read that the salad should be the size of the bunny’s head, but that doesn’t work for us — Kieko can handle a salad 4 times the size of her small head, but Moshi must have less than the size of his big smooshy face or there will be mushy poop smeared everywhere!