Well, it depends really on where you're buying them. I've had completely useless and super potent seeds come from the same place. The amount you need (thus the potency of the seeds) will vary greatly from batch to batch if you don't have a steady source of the exact same seeds.
I'd say a good starting point is about 150 grams, and work your way up from there. Depending on your opiate tolerance and the strength of the seeds you have, you could need more or even less. You've given me no information to answer your question with, as no two people will get the exact same effects from the same dose of any given drug.
Like I was saying, seed potency is notorious for being wildly differential from batch to batch, even from the same source. Color of the tea is somewhat (albeit unreliable 100% of the time) a gauge of potency, bitterness is another. The tea you get should be a brownish-yellow color. If it's milky, and whitish-yellow you let the seeds sit in the water for too long. This is not a 'tea' that you steep, but an 'infusion' that you wash.