I can't understand your sentence, " Don't invest more than you can afford to lose " and "invest as much as you like. " I assume you are treating investment is like gambling because you are willing to lose the money that you invested. I know investing your money is a risk, but you shouldn't let all of your money lose.
I think if OP would like to start a day trading, a 100$ is enough because it is also the same amount that I started from trading in cryptocurrencies, and he can be able to gain profit from that kind of amount, as long he is willing to calculate the risks.