I think it would be best for you to come up with 2 plans so you can really reach your dream business.
If I were you, this is what I would do.
Plan A. If you have the option to invest, invest but don't spend it all, just a small amount and then while you invest, do another job so that somehow you have extra funds to reach your goal of $20,000 for in your dream business.
Plan B. If your investment fails , at least it won't hurt too much because you didn't spend it all, and that's where your extra funds will come in to start over. Always be ready for what happens
And I think don't stay at $20,000. Increase your budget because this is your dream.
It is always better to have spare funds
You shared exactly what I had on my mind and was going to write, but I was also going to talk about where you should invest, It will not be investment advice but a suggestion so please DYOR too. I would say, Invest in BTC for the long term. Because OP was saying it is hard for his friend to make $5,000 and it will take him some time to save that much money. Like a long time. If that's the case, then simply invest some of his savings in BTC and wait for the long term.
Like doing holding, you will be earning on your investment while you will be doing the work and making savings too. In this way, you will have more than one earning source and the amount of $5,000 will not be that much hard to make. If your friend is not a BTC user or does not trust it, then tell him to now trust on ALTs too. Because ALTs are way risky.
Tell him to, find a way which in his own thoughts is good and he thinks that, this would make him some money. But every good business need huge investment, so to start a small work, OP should use his smartness.