If you can swing it in you budget, get yourself a Mega+ unit. As far as what units to get and where to put them, it really depends on your style of fishing and what transducer you put on your trolling motor. I mounted a SI unit on my console and a DI on my bow. I have built in DI on my trolling motor so I needed the DI unit on the bow to use it. I can view SI on the bow unit from the transom mounted transducer as I have the two units networked. I walleye fish so I don’t have the need for SI transducer on my trolling motor in my opinion. I like to be able to use the SI to scout for structure and fish before putting the trolling motor down.