Hi @Cuzer,
- You do not need to use Ableton Link to use multiple DJ controllers with djay. This is used when you want to sync multiple software applications together.
- You can simply connect multiple MIDI controllers to your laptop or iPad and use them together with djay. You either need a device with multiple USB ports (most Windows laptops have this) or a powered USB hub. If your iPad is has a USB-C port, you will need a powered USB-C hub. There are lots of options out there and there is an existing discussion here: Adapter Advice Please - iPad Air and Hercules Starlight - #3 by Slak_Jaw
I hope that helps!