I think it really depends on how much $$$ you want to spend . Unless your going to buy a combo with a 8" or larger screen I would buy 2 units . I picked up a nice Ray DS500 on sale at Bethel marine and plan on buying a Garmin GPS this spring . I am never a big fan of putting all my eggs in 1 basket , so I like knowing if one unit is going in for service I will still have the other. And I will do it for well under a $1k .
On the transducer do you mean setting the puck inside the hull and letting it shoot thur the fiberglass or drilling a hole in the bottom with a hull mounted transducer?
The best I believe would be , hull mount , transom mount and then thur the hull .
Good Luck !