Bogleheads forum [0] and wiki [1] are pretty sensible resources in general.

[0] https://www.bogleheads.org/

[1] https://www.bogleheads.org/wiki/Bogleheads%C2%AE_investment_...

Some recommended resources:

reddit.com/r/financialindependence/ (check out all the links in the sidebar). The advice on this sub is generally much higher quality than r/personalfinance (although less newbie friendly)

See also: Mr. Money Mustache / Dave Ramsey (both seriously tackle the behavior problems that hold us back from success and wealth)

Good starting point: https://www.reddit.com/r/personalfinance/wiki/index

There are universal themes like budgeting, responsible spending, paying yourself before you pay others, etc. Just remember that everyone's situation and priorities are different, so don't get caught up in one specific strategy.

books, research reports, personal experience.

The last is vital, as an investor's emotional composure is at times even more important than the rational side of investing.

Why spend the time learning about investing beyond the basics if you could be researching a niche in your field to double or add a zero to your income? It doesn't seem worth it to me if you don't have connections within the industry. You're still a retail investor at the end of the day compared to professionals at banks (which honestly, will have better information), so why not just use Vanguard stuff unless you want to go pro?

Because you need the mental fortitude to not liquidate your ETFs in the next crash.

edit: that being said, what you said is what I almost always tell friends who have the temptation to augment their income through side projects.