Starting an Online Business as a Beginner

This is a very personal topic for me, because I have propably made all possible mistakes that you should not do when starting. My business is founded 2014. Of course I picked shiny objects to sell. They were so cool. The mistake was that they were too expensive to buy and too technical to sell. With the knowledge that I now have, I would pick cheap items to sell (I have already done that some years ago). If you sell expensive items your investment to your stock is much heavier.

The second mistake was that I choosed an platform that was too expensive for my e-store. Now I know that you don't have to sell products in your own store, you don't have to buy stock, you don't even need to pay for a website.

Third mistake was that I paid too high costs for advertising.

Improvement of all these mistakes has taken many years, so I think it would be a nice thing to tell other beginners what to do. This is for you, if you have not much money to invest and are desperately seeking a way to start business online.
In my opinion you need before everything else good step-by-step advice, what to do. Secondly, these advice should cost as little as possible.