The "classic" ECA stack dosage is:
25mg Ephedrine, 200mg Caffeine, 100/200mg Aspirin
50mg is a higher dose than most beginners can tolerate in one dosage. 25mg Ephedrine 3x a day is fine. Dont push it over 100mg total daily, especially if you are older.
Although I'm sure Satchboogie and a few others would have you take 50-100mg in one dose, these are the people that reccommend it to the wrong person and then someone has a heart attack.
Pure Ephedrine HCL is better than Ephedra alkaloids. You can get pure Ephedrine HCL cheaply if you buy the 8mg tablets from Canada. Customs will most certainly open and log the # of bottles you ordered, then seal it and ship it to you. They wont send you a notice or anything, they just do this to make sure you arent ordering many bottles to make drugz with. So keep the orders to 1-3 bottles and infrequent, like every couple of months. You could always have your friends order them as well.