I've built and run several configs over the years and now have a Ranger bass boat w/2-12" and 1-16" graph, forward facing sonar, 2 ducers at the stern, external GPS, and I replaced all the factory wiring. One question - do you have a helm graph and what is it?
This is what I recommend:
Go with a Humminbird, that way you'll be able to use all the functions. The HELIX models (w/CHIRP) would be the best place to start unless you want a touch-screen. Size is important because at the bow, the graph will be located down around your feet.
The Terrova has a transducer that you should utilize - make sure the graph is compatible (IE. Dual Spectrum CHIRP) etc
Phone apps are not the best for operating the Terrova (they are slow and only include a few controls - or at least they did), plus you wont want to drop your phone overboard trying to use it to control the terrova! Terrova remote or the controls on the graph (if networked) are the best.
Ensure that the graph has networking ability to you can connect it to your graphs, etc, either now or in the future.
Depending on the bow graph you select you'll have to consider the quality of power you bring to it. The more powerful the graph, the more important this becomes.
If you need any further help, PM me and i'd be more than happy to have a phone conversation on any questions you may have.