If your friend believes in the technology behind BCH & what it intends to accomplish in the future then investing a lump sum followed by dollar cost averaging over time is a good idea.
Best way to buy is little by little. If I had taken this advice and bought just $20 a week since I found out about bitcoin in 2013 I'd be a millionaire today.
I second the other responders sentiment. However, it's looking pretty bullish. BTC is going to hit real hard resistance around $7,250 though. I think we'll come back down with it.