I think If you have only 500$, it's better to invest in 1-2 ICO.
If to coins, then, Ethereum, Cardano, Litecoin, Stellar, NEO are great options that will grow!
I don't agree, 500$ is very small amount and with that OP should look for undervalued low cap altcoins with active team and solid future.
Stellar is good, it has bright future and active team but I am not so sure that it will grow big. OP should look for coins which are under half dollar.