Alkaloid content can vary widely depending on a whole host of factors (variety, age, growing conditions, stress, etc).
Erowid lists a common dosage of fresh peyote as between 100-150 grams, or roughly 6-12 mid sized buttons.
I'd probably aim for 10+ buttons or closer to the 150 gram weight to get fully psychedelic effects. I'd definitely just eat the fresh buttons, save the teas and other prep methods for dried material.