As others have said, only risk what you are willing to lose. But anywhere from $100-$1000 would be a great initial investment, as long as you don't want to buy bitcoin (because the transfer fees would eat way at your initial deposit).

I'm currently using Kucoin and Binance as my main exchanges, they have good liquidity, and a lot of decent coins. As for coin recommendations, I would suggest Deepbrain Chain (DBC), Oyster Pearl (PRL), Raiblocks (XRB) and NEO. All of which are available on Kucoin. Please research them more yourself, but I think all have the potential to at least double in value in the next few months.

If you want anymore details, just let me know.