For my first time with powdered Peruvian Torch, I went with 25g, and that was a moderate trip. Given potential differences in strength, it would probably be best to take 25-30g of any new batch, and figure out subsequent dosages from there.
As for preparation methods, I stirred the powder into 20 ounces or so of orange juice (add the powder first, then pour the juice into it to prevent it from clumping up). The texture wasn't too bad at that level, and the taste was far less awful than I'd expected. You can use orange juice or lemonade (or a similarly acidic beverage) as a chaser in between sips of cactus; the acidity kills most of the aftertaste (as the alkaloids themselves are responsible for most of the bitterness).
As for preparation methods, I stirred the powder into 20 ounces or so of orange juice (add the powder first, then pour the juice into it to prevent it from clumping up). The texture wasn't too bad at that level, and the taste was far less awful than I'd expected. You can use orange juice or lemonade (or a similarly acidic beverage) as a chaser in between sips of cactus; the acidity kills most of the aftertaste (as the alkaloids themselves are responsible for most of the bitterness).