There are plenty of helpfull videos on youtube on fitting transducers.
I run both the standard transom mount and side-scan which hold bottom extremely well at my cruise speed of around 40kmh (20 knts). I have no problems in deep water 500m + but need to be moving much slower.
Ive owned bigger 1 kw transducers on previous boats and also cut holes through the hull before to fit some. The standard transom mount is as good as any in my opinion.
The transducer can often through spray back over the enegine and in the case of my Yamaha this can end up getting through the air intakes on the cowling. You can buy a spray deflector or as in my image I just cut up an old leaky fuel can to the size and shape I needed.
For water shallower than 300m I kept mine on 200htz.
Holding bottom at 40kmh