If you want to build up wealth and have a safety net of income it's recommended that you have at least 2 streams of income.
But if you can have more than 2 streams of income coming in that would also be better since you're not relying on just one single source of income.
For example you could start investing in rental properties so that you can have rental income coming to you while you still work your current job.
That way if the job you have goes under and you lose the job then you'd still have an income source.
Or you could also start a website or blog and while you're working on your current job you could write blog posts in the evenings or on the weekends when you're off your regular job.
That's what I did and almost 6 years after starting my blog and blogging part time when I was not at work I built up a blog that 6 years later I was able to live off the income from the blog alone and quit my job to focus solely on the blog.
Blogging actually now brings in more income than my job did and I work half the hours on the blog.
The money I make is now residual and passive income and I wake up in the morning and make more money than my day job made me.
I blog about 3 times per week now and the blog continues to bring in a nice income and hopefully will for years to come.