Amazon holds less and less inventory each year. I don't think that they really want to own inventory for resale any longer. Their retail operations make money on warehousing, commissions on sales, distribution, and raping the USPS on last mile delivery. They don't need to tie up cash on goods and can make their money across the rest of the fulfillment chain.

Speaking of distribution, Amazon employs a ton of folks highly skilled in creating and running distribution networks. They're building out a secure network for prescription medications right now. In many ways they compete with UPS and Fedex, even as they partner with them. Once they have nation-wide last mile delivery, expect the USPS to have their legs cut out from under them unless USPS is willing to continue delivering packages at a loss. Amazon already has a business model for warehousing and delivering last-mile delivery. They see to operate like a franchisee.

The most profitable line of business is probably Prime memberships. Especially now that the service is more about digital services (high fixed costs, almost no variable cost per subscriber) and less about shipping (I haven't gotten a next day package in a couple years, and 2 day delivery is now rare).

Amazon Web Services profit is booming. They have like 1/3 of the "cloud" market and it's rapidly growing. Operating income was up nearly 80% one recent quarter.

I don't think Made in China tariffs are much of a threat to Amazon, beyond the COGS for their Amazon branded stuff or the price of equipment for AWS. If the price of goods goes up, their commission on sales goes up. They might ship a little less, but that's it. The rest of their business line is pretty much tariff agnostic.