Spiro is only good for androgenic hirsutism, which is usually what it is. If you were born with a lot of vellus hair, like my daughter has, that will not be helped with Spiro. She's got it all over her back, but it's really light. Again, no androgen involvement there. PCOS *is* hormonal, Spiro can help with that--just as it can help with androgen sensitivity.
You will need *at least* 100 mg/day... but I daresay you will need 200 mg/day. Start out slowly and you shouldn't have side effects. Start with 25 mg for a few days, then 50 mg per day for a few days(divided), then 100 for a week or two, then 150-200 mg/day after that from then on. Best taken with food, but not necessary.
For people who only need it for acne or oily skin/scalp, 50 mg/day is sufficient. That small amount is not sufficient for hirsutism.