With the Ultrex I would go with Humminbird Units at the console and the large Garmin for the Livescope and the other Hbird for the Mega 360. You really only need one unit at the console because they network with each other (Ultrex, Mega360, Fish Finders).

I assume your Garmin will be the standalone LS unit. I agree with SuperDave to get the biggest you can afford.