A small amount to invest is fine and I think it is that simple. You should check with the creators of the coin for the official rules...each coin could have different rules.
I know the risks of losing money with an ICO, but I think it is worth to try for long term.
So if you know the risks why do you want to invest in
this coin. Why is this coin of the 200+ others
the coin you want to participate in? What about it is different or better than the established Bitcoin, Litecoin, Ether, Dash, and Monero?
ICOs fail significantly more often than they succeed. And they rarely jump to real levels of price like other established coins have, so the risk you're taking doesn't even match the likely upside potential.
You should watch
Ben Perrin's BTC Sessions video on an ICO before you invest in this coin.