You could try 25mg a day for about five days to see if you get anything from it. If not, then up the dosage. You may find out that don't even get anything off of 30mg a day.
I find 50mg each day is perfect. I take 10mg approx every 3 - 4 hours and get great results. I have tried 30 and 35 and did not achieve anything like i do on 50mg. I know that may be obvious but everyone is different.
at least 30 IMO....i've done less with minimal results but that may not be the case for you..shoot low and see what works (but i wouldn't start at less than 30)