Hi nelusan.
I tried this 2 Hugo themes with integrated e-commerce platforms: vex and hargo.
The e-commece integration works through snipcart, so you need to have an account there. Concretely you need to add an api-key in your Hugo code (for vex you can do it directly in the config.toml file, for hargo if i remember right it is in theme/layouts/partials/head.html).
Snipcart charge you with 2% of your sales (but minimum 10$/month). Then you need to choose a payment gateway (ex. paypal, stripe, etc.) for the management of payment with credit cards. They charge you another 2-3% + some cents for every transactions (or only paypal checkout for free).
You can do your site completely with Rblogdown and Hugo, but you manage all the e-commerce side directly in snipcart (it is relatively simple and well documented). And you can set snipcart in test-mode, so you can do your trials.
Sorry for bad english 