How do I connect all my USB 3 devices to a new Mac mini from a 2013 iMac?

The Mac mini has two USB-C ports and three Thunderbolt/USB-C ports.

Mac mini - Technical Specifications - Apple

Your USB-A devices can be connected to the mini with a hub that connects to the mini with a USB-C cable and has USB-A ports on it, or you can use USB-A to USB-C adapters or cables with your individual USB devices.

Search Amazon or google for "USB-A to USB-C adapter", and also look for "USB-C hub or dock".

If you decide to go the way of a hub, look for one that is powered by an ac power adapter. These can provide plenty of juice for any USB device that might require it.

i would recommend looking at one of OWC’s Devices. You can contact them at macsales.com. I strongly recommend talking to them on the phone so they get a more clear idea of what you attempting to accomplish!!!!!