Is it okay to invest $50-100 into different ETFs or focus on a few with $100-200 into each?

Improving from what Chris mentioned,
You need to look if there is any crossover or similarities between the ETFs. If u overdiversified, along with a need to pay commission, you cost will be hefty and your upside reward is heavily compromised.
This is assuming that u do not know how to optimise your portfolio.

Taking account into Chris, I would recommend u to use roboadvisors while u learn how to fine pick ETF.

Assuming u want your cost to be <=1%.
If the trading cost is $25, then u need >= $2500 per trade transaction

Etf alone is made to be diversified. If you want to further protect your risk, and taking into Chris recommendation, my recommendation is to use roboadvisors

An alternative would be to invest through a robo-advisor like Syfe. Each Syfe portfolio holds about 15 ETFs and your investment would give you exposure to all 15 ETFs directly. There are no brokerage fees or trading costs that you have to pay.