The follow up questions have little to no relation to your original post. To expect help from members it is best to create a new topic thread for any new topics so readers in the future can understand the logical thinking from problem to resolution.
For your fishfinder, I would recommend running the setup wizard and seeing if it is recognized there. If not then look a the sounder light and tell us what it is doing. (Off, flashing fast, flashing slowly 1 sec on 1 sec off)
If the fish finder shows in the setup wizard you are in good shape. Save and exit then go to the fish finder menu and select the sounder source and it should work.