BMO,
If you put another HDS in the bow your waypoints are shared automatically with your bow mounted unit.
I have an HDS 10 at the helm and an HDS 7 up front. I have both of them running most of the time. When trolling for walleyes, although I am in the back of the boat, it is actually easier to look up front and see the bow mount as apposed to staring around the seated passenger to look at the helm unit.
You already have structure scan so if you mount another HDS unit up front, you simply connect them through an Ethernet cable tied to your LSS module.
I have a Minn Kota with a universal sonar built in. It is hooked to my bow mounted unit. Obviously, you can have whatever you want.
One issue I have found is when you tie the units together and have both running at the same time, you can only utilize one of the transducers (regular and not the structure scan). If I am at the bow, I can select the bow mounted transducer. Unfortunately, it will change the transducer setting on my HDS 10 unit. I was originally under the impression that each unit could run off from both or different ones at the same time. Not a big deal however as I normally run off from my back transducer.
Another issue is that the front unit doesn't pull temperature. Although there is a sensor on the rear transducer, something gets lost in translation when it runs through the network.
If it were me, I would go with another 7 unit. I have a 10, and 8, two 7's and an HDS 5. In my opinion, the 5 just doesn't cut it. It doesn't run split screen very well at all.
One last thing. Make sure that you tie all of your "yellow" power wires together (one from your helm unit, one from your bow unit, and one from your LSS module). This the "wake up" wire. It ensures that when your units are powered off, the LSS module is NOT powered up. It will "wake" it up when you turn one of the units on.
I have OCD "Obsessive Crappie Disorder"