All CS benchmarks are situational depending on who you are laning against/how much you've been roaming. However, you should always aim for AT LEAST 100 CS at 15 minutes, and at least 200 at 30. It's really not that difficult, and if you stay in lane for most of the time you shouldn't have a problem with it.

100 creeps come out by the 10:00 min mark, i always try to aim for as high % as possible by the 10 min marks. Like if by the 10 min mark i have 70 cs thats a 70%. So test yourself see what last hit % youre getting :P