If I was wanting to stay on a particular spot, GPS for sure. They are built in the units now days.
Downimaging only works if the boat is moving. It's not a good picture unless you're moving over a certain mile per hour. I think it's .5 or .7mph? At least for Lowrance it is.
I have the ability to use side scan, downscan, sonar, and mapping on my 7" screen on the bow but honestly, I don't use side imaging or down imaging that often. When I do, it's too hard to see at that size and my structure /down imaging transducer is at the back of the boat, not the front. In your application, it would be on the front.
Chirp sonar is a higher defined sonar image. If I were to get one as you're describing, chirp sonar and gps is the way I would go. But I don't think Birds offer chirp technology yet.