connect 2 external Hard Drives

Most external mechanical hard drives connect via USB protocol. As long as you're talking about that, it's easy to go between USB-C connectors and USB-A ones, in either direction. Mechanical hard drives are slow enough that once you get up to USB 3.0 or better, it's the drive (or software) – not the interface – that bottlenecks performance.

External SSDs may require either USB or Thunderbolt connections. Some external SSDs that use USB protocol can connect at speeds greater than those of USB 3.0 and therefore will benefit from being connected to one of a Mac's USB-C ports (which typically can run at USB 3.1 Gen 2 speeds), even if they'll work with USB-A (USB 3.0) ones.

If you eventually chose the usb hub way in order to save ports on your mac, ensure you chose a powered one.

If you use two devices attached through one port at the same time, they'll compete for the available bandwidth.

So if you were copying large amounts of data from one Thunderbolt 3 or USB-C (USB 3.1 Gen 2) SSD to another, where each drive could individually use a lot of the bandwidth of Thunderbolt 3 or of USB 3.1 Gen 2, there might be a case for using separate ports.

You might put Thunderbolt 3 SSDs on a different port than a 5K or 6K Thunderbolt monitor for the same reason.

For most stuff, people do just fine with connecting a lot of stuff through one port.