Switching to a new unit…wiring?

I’m possibly buying a used boat that has an 1198 on the stern and a 958 on the bow that are networked together along with the terrova via Ethernet/switch box. My question is if I upgrade the units in the future, would it be as simple as plugging the ethernet cables into the new units and I would be good to go? I know I’d have to switch transducers etc, but I’m just concerned with connectivity.

Also, I may add my current Garmin unit so I’d have two locators on the stern. Would I experience interference issues if I did that?

No idea on the Garmin units but if you buy hummingbird units to replace the existing units you should be able to use the existing network switch and cables. You may also need to get “dongle” adaptors for the end of each cable to connect to the newer units, to convert from the round threaded plug style to the newer square push on plug but I might be incorrect on that part.