I’m interested in becoming a seller on Amazon

So, I think it works like this, right?

You buy products, typically in bulk from a wholesaler, then sell them on amazon for a markup.

Questions I have:

•Who do I contact to buy products in bulk to re-sell? Say, books for example, as I just read a bit of the book selling article on Amazon’s “Seller University”.

•How much capitol would I typically need to make a purchase from a wholesaler?

•What are the categories of products to sell with the lowest risk and most upside?

•Do you typically just stick with one category of products, or diversify your stock?

•Anything else I should know before learning how to become an Amazon seller?

I’d appreciate any useful advice or info you can provide. I’m 19, and used to sell candy in middle school, but that’s the extent of my business experience. I have also watched lots of Shark Tank.