Investing in stocks as supplemental income?

So im a medical resident with 2 years left and been investing in VOO since college. I have about 15k in it and plan to invest 3-4k a month of my monthly income once I finish residency until retirement.

I know this may be frowned upon here but I also set aside some money as "fun money." Stuff to invest in like up and coming stocks, swing trading forex. Money I am 100% comfortable losing.

At the same time, I don't want to just gamble. For the "fun money," what's the smartest way to go about it? Would technical analysis be best or trying to flip stocks using methods that Warren Buffet talked about to find undervalued stocks. I think it would be great to find a way to have some supplemental income and at the worst case scenario, I learn fundamental analysis.

I just don't know how to approach the fun money investing and what skillset I should be learning!