Don't try to run side-scan from a TM mounted transducer. It doesn't work very well for some technical reasons I won't go into here, but trust me on that, LOL.

I'm a Lowrance guy, so can't speak to the other brands. Any current HDS model will do what you need (9 inch and up), stand-alone, no other modules needed. There's a combo 2D & down-scan transducer with temp. available that fits Minn Kota 36V motors nicely. There's an excellent protective bracket available from Transducer Saver. No other transducer or box is needed for this setup, but you won't have side-scan. (Side-scan is best observed while at trolling speed at the console.)

The Minn Kota nosecone transducers work with an adapter cable. It's a nice backup plan in case the combo transducer gets trashed while fishing. Mine is set up for plan B with a simple cable swap.

With Lowrance, I recommend the external antenna and heading sensor - specifically for the heading sensor. This stops the map view from rotating if you sit still on a spot. It will allow the map to stay oriented with reference to the bow of your boat. This is very desirable to see where waypoints are so you can cast toward them accurately. If you add this feature, you'll need to set up a NMEA network to connect it (not hard, not very much $)