I got started with my endeavors from people explaining things to me on programming IRC channels, so despite its bad reputation, advice from random strangers on the internet can be good advice.
As for this particular project, I stopped it when I ran out of bikinis and couldn't buy more at the same conditions anymore. At the same time, competition from China was also arriving in the form of dropshipping. I could have switched suppliers to reduce my purchase costs and remain competitive, but selling a high volume of cheap products is a lot more work than selling a low volume of high priced items.
All the best with your side business (and all)!