2 and 3 are not bad but 1 is garbage to be honest.
1. Invest in Bitcoin with your spare money:
I can say that this advice is not necessary in today's bitcoin world. This advice was only relevant like a decade ago when bitcoin was been seen with alot of skepticism. Some saw bitcoin as gambling, some saw it as a ponze scheme while others saw it as a bubble the will burst.
In today's bitcoin, we know that if you invest with your spare money you may never make any fortune from bitcoin.
And not only for Bitcoin investment, but for investment in general, if you do not invest with your spare money, you will either invest with money that you will lack in the short term, or you will go into debt to invest and both options have a high probability of going wrong due to the volatility of Bitcoin.
Advice 1 still stands.
Warren Buffet, a renowned investor was not actually investing what he is able to lose, that was why he became super rich. He was instead investing in early start ups and having large returns. He was using the principle of