Whatever you do start your own side business. That is the most important advice in life. If you have a side business even you loose your job you can still make money and develop your business into a full-time job. If you work a full-time job then it gives ou extra income and safety.
There is nothing more important than having a side business!
If you work full time, then you have your own extra business very hard. Therefore, you need to look for a passive source of income. But the problem is that you need to have an initial capital for this
VasyaPupkin is right having to manage a business together with having a full-time job is an impossible task not unless you have help with your business. That is how businesses works "you let your hard earned money" work for you in a way which you hire people to manage your own business. Well also I think that is the key in order to have a stable income hire the right people to manage your business and observe if it is growing right behind their backs, even having a full-time job is still considered a temporary solution but if you have a 2nd line of income like a business then you are good to go.