What is a good amount of money to invest into Ethereum?

I am a beginner and really want to get into trading cryptocurrencies and sometime later, stocks. I'm 18 and just got my state ID and have about $300 dollars to my name at the moment. I use Trading View with Hull Suite and Super Trend indicators on using the 5 minute chart. I don't necessarily want to become rich (yet) so I'd like to be realistic with it and just want to make a nice passive income and slowly save up from there and start to put more money into the market.

So what I was thinking was around 50 to 100 dollars and hopefully soon, 500. Would that be a good investment short term for day trading ETH? If you have something better in mind them please, lay it on me I would love to hear what yall got to say.

Also yall got any good US exchanges with low fees in mind too? So far I'v only got verified on FTX US and still working on it with KuCoin and Kraken. Thanks.