So, going off of the first post..
Awesome you are going to get paper maps and a compass.
You need a unit that utilizes GPS and not a cell tower generated location.
You want a unit that is water proof, not water resistant, water proof, I think the rating is IP67, good for immersion to 1 meter for 30 minutes, I think I have that right but you get my point.
The screen needs to be readily readable in direct sunlight, and yet has a night setting to limit the erosion of your night vision-red flash lights are also desirable for night usage and reading maps.
Since the Yamaha boats do not utilize a NEMA 2000 bus, I do not think that you will be able to display engine gauges, fuel level etc. Go and have a look at @zackadams posts for his 252 FSH. I believe he set up a NEMA bus but only for his Simrad head unit, trolling motor and radar.
Mapping-I have a Solix 10” and use Lake Master chips. These are very good maps, and the plotter / chart page has the ability to set water offset or the current depth of the water, you look up your lake say on the USBR page and fInd the current depth, compare that to the full pool depth and then set the water off set. Say the lake is 10’ down, you’d set the water offset at -10. You mentioned Mead and Powell, both are down a lot right now but will be coming back up, these waters are treacherous as the water lowers, they call the big boulders white whales. But the main thing is being able to set the water level at whatever number of feet below full pool, this changes the landscape dramatically. Also, in my unit, you can set a couple of highlight depths, the important one for you is the shallow water setting, which has a audible alarm if you so desire, if you don’t you don’t have to have it, but this shallow water alarm can be set for any depth regardless of your shallow water shading. Anyway, having the red highlighted shallow water is great, I set it to 10’ or less when I was at Powell last summer when the water was 150’ low, at my home lakes I run it at 5’. You can also set the highlighted depths so to speak for deep blue for shallow up to light blue as the water gets shallower. On this mapping page, you can also have; source voltage, speed over ground, course over ground, depth, water temp and time, again, you choose what you want to see. As you travel it leaves a track behind the little boat avatar on the screen, allows you to save tracks, like a known safe track out of your portage. I can tell you that as the water level has dropped at some of the local reservoirs that are intended for farming, and the water level is down 18‘ at one of them, having that level of definition of the reservoirs depths is pretty darn useful.
Transducer-I get you do not want to fish, the transducer not only shows depth it also shows water temp. While the unit does have 2D sonar, it also has down imaging and side imaging. You may not think that these pages would serve you, consider this, while a depth meter / sonar shows depth, the 2D sonar shows the bottom, the down imaging shows structures like trees, rocks, etc.. pretty amazing stuff. Same with the side imaging, amazing views of the bottom structure. Might be pretty useful pages when you are out exploring. I use the DI when pulling into a cove and want to go swimming, I can see trees, grass etc. The transducer shows depth and you can check that against your chart while on the water to verify the accuracy of the reported water depth at a given location.
The nice thing about making an investment in a MFD that is expensive, is that when you decide to move to another boat, you just take it with you, leaving only the wiring and transducer with the boat.
The VHF radio you choose, whether portable or fixed mounted should display the gps coordinates at any give time. The hand held portable units are limited to 5 watts, the base units are 26 watts of transmit power. You will need an antenna of at least 4’ in length to get an appreciable distance. If you are short on dash real estate, and want the power of the base unit, ICOM I think makes a base unit who‘s main head is mounted in a cabinet the microphone is a command mike with on/off, channel selector, gps coordinates etc.. other than the mic itself, the only thing on the dash is a port to plug the mic into. I can tell you from experience that the hand held radios are pretty limited as far as range. I’ll be putting a base station on my boat this winter, probably one of those ICOM radios I mentioned.
Getting help-While the vhf radio is good, a gps based emergency locator beacon is the way to go. There are several on the market, the marine based ones are probably the best. But Garmin makes a unit called InReach and uses your cell phone via Bluetooth to communicate via satellite and there is a subscription involved. For your case an ACR
ACR ResQLink 400 PLB – Floating Personal Locator Beacon | The GPS Store might be better, just keep it on the boat and when you need it pull out the antenna and hit the button, even has a strobe I believe. For comms, if you were going to be a ways out, like on Powell, renting a SAT phone is the way to go.
For traveling at night, most likely you are not going to be on plane, but you still need to see, so a hand held spot light that will work off of the boats electrical system would be good to have. There some excellent LED spot lights out there. I have an old Q Beam, 1 million candle power (thats how they used to measure lights brightness) hand held light that runs off of the 12V power point. This a simple solution that doesn’t take up hardly any space, you can run the light while driving or your co pilot can hold it.
Having a ditch bag / go bag is a good idea as well. One bag that you can grab that will have the essentials needed to survive until help arrives. These are not cheap, none of this stuff is. My solution is dry bags, I can easily clip there straps together and they will float.
Here’s a saying I once heard that I thought was great. I had said I’d rather be lucky than good, a colleague nearby heard that and said “Luck favors those that are prepared”. I just love that saying.
You’ve got ambitious fun plans, with a little bit of preparation, and arguably some serious coin, you will be prepared for a bad day that hopefully never comes. But if it does come you will have made the preparations to live through it in relative comfort and tell the tale.
