You can learn from watching streams.. atleast i did
not only csing, but also map awerness (or how its written xD) etc,, you see what combo's work well togetter etc and some streamers comment their streams, which can be some helpfull sometimes.
CS is important no matter what, and you can push and farm at the same time... it will be a bit slower but you'll have more money > more items = more power or more sustain ^^