Big e-commerce website

Hi everybody,
At the first sorry for my bad English.
I'm interesting in e-commerce, so I want to do something like Amazon but not worldwide I want to focus in one country, of course I understand that I can't be a concurrent of big sites like Amazon or Aliexpress but everything has a start so for that I need some help or ideas :
-There is any secure open source software to do like those sites?
- Supposed my site and all technical issues is done, how I can have some products to sell in my site? I have limited budget? I order 3 or 5 for 10 products and I start promoting my site?
-What do you think about this idea, when we have a limited budget?
In advance thank you

Heard a bunch of people recommend Shopify
And in terms of stock, you search around on cheap sites for niche items you believe might sell well (Do google keyword search) and purchase them in bulk for resale.

Shopify is good and easy to use. Magento is very popular for larger stores but you will need to be technically proficient. Whatever you decide to sell, make sure there is demand, it's competitively priced, or it's rare/unique to yourself in that particular market.

Look into SEO (Search Engine Optimization) and ads to get traffic, and make sure the design, grammar and spelling is on point otherwise you look like a scam.

Deal Xtreme have always been a decent website to buy some cheap bulk items from to sell on for a profit,