Audio Interface for Outboard Gear and general question

Hi all! Im new to mixing and engineering and currently running on a Mac Studio M1 with the Apogee duet 3

I just recently bought the avalon 737 which will be connected directly to the interface.

I dont understand the concept of interfaces with multiple in and outs and patchbays and what they are usefull for as I am a complete newbie…

I wonder if I have to replace my apogee duet 3 if i want to lets say get more outboard gear in the future or if i could connect a patchbay to my duet 3 or if that doesnt work.

Please go easy on me since I really have zero clue and I will start to produce in the box first but I like to gather knowledge for the future when I feel like going more hybrid cheers!