My question to you, are you going to Boon Dock or not?
If you are not than I would stick with just one good 12V battery, less weight is better when cargo capacity is concerned for storage. I use a 12V NAPA battery made by East Penn MFG CO. I have had my residential fridge since 2015 and I have never have had spoiled food do to towing our trailer. The battery will provide enough electrical power through the inverter to operate the fridge for one day if fully charged. We also do not Boon Dock choosing instead to stay at 50AMP full service campsite when traveling. The battery will be fully charged by the next day by the converter when we set out to travel for the next day.
I see no need for Solar Panels if you are not planning on Boon Docking. Extra expense and weight plus an obtrusion into the sealed roof were a leak can occur.
Your dual 440 AMP alternator will maintain the battery in the trailer, but not charge it! Why, the wire in the harness for the 7-pin connector is not large (diameter) enough to carry the charge load required to charge a battery.
I personally prefer the 12 gal stored hot water tank that is gas/electric instead of the on demand units! We will use the gas to initially heat the water for the first time and than switch over to the electrical heating element to maintain the water temps.
Regardless where you camp the third A/C is a great option to have. There has been times we could have used a third A/C unit in our Cedar Creek.
I would also look at if still available as an option an awing on the dining room slide room. This will help in keeping the unit cool and provide more shade to sit under when the sun is on the curb side.
If the TrailAir King pin box is still an option I would order that too. This will improve your towing experience as there will be less up and down motion that is felt in the tow vehicle!
2016 34RL CC; 2008 Ram Mega Cab 2500HD, 6.7L, 68RFE 6 speed, 4X4, Smarty S67, TDR 135K+miles