If you buy some now, you will get extra coin after the fork 
that's something to look for too 
that's something to look for too I've heard of ethereum fork, is it like bitcoin fork that produces bitcoin cash?
if so, would the extra coin of ethereum fork be a new coin?
Nah I don't think so as this ethereum fork will be just to upgrade the network so as to make transaction faster than before. But there will be no airdrop coin from this fork as you asked.
when bitcoin fork everyone get free a coin so the price increase, but when eth fork everyone does not get anything, so maybe eth price will increase like bitcoin price or not? I still confused to buy eth now or not
