There are very minimal requirements for running Commerce on your website.
To accept real transactions in live mode you must:
Configure at least one Payment Integration.
Provide valid billing details to Commerce in your Billing Settings.
Pricing details coming soon.
Run your website via https to protect customer credentials.
If you fail to do so Commerce will not load and will output the following console error:
"Commerce in 'live' mode must be run under 'https'"
Our default User Interface is responsive and scales for Mobile/Tablet/Desktop.
So that it can do so, ensure your own site is responsive and has an appropriate meta tag in the head.
<meta name="viewport" content="width=device-width,initial-scale=1.0">