Hello
The brand of the USB HDD doesn't matter (WD, Seagate, Freecom, Samsung, etc.), but it should be of good quality. For higher demands, there are also more expensive types, especially for professional continuous use (but not necessary here in my opinion).

Hello
I have 2 buffalo HD-HX2.0TU3s with 2 TB each connected. They have been running absolutely flawlessly since day one (10 months by now) and are more or less in constant use.
But it basically works with every external HD, at least up to 4 TB.

Hello, I do not have a hard disc connected to the technisat. I need the Samsung Portable T7 for backups, I can recommend it.