If you will have a microwave on an inverter- go with 24v (or any other high load 120v items - hairdryers,etc).
Yes. To a point.
This makes me think I should stick with 12V due to the availability of appliances and loads, but I'm considering 24V so that I could run smaller cables and possible add more batteries/loads later on.
If you ever add a microwave don’t buy a huge one. 12V is good to 2000W; 3000W steady is past what you should do for 12V systems.
An intermittent load like a smaller microwave could require 3000W inverter for startup surge, but run at 1200W or maybe less.
That you don’t have a microwave now, and you were traveling in a native 12 V system vehicle, I couldn’t come up with any reason to go 24 V in your situation. In my opinion, even if you add a microwave in the future, I would still stay with 12 V in your situation.
Yes the cable cost will be significantly higher by percentage. However, on the grand scale of things the dollars really aren’t that significant to cable up for 250 Amps. If you never can imagine adding a microwave then staying 12 V is a no-brainer.
In my experience a 2000Watt pure sine inverter will more than handle anything you could throw at it from a shop vac to a refrigerator. And with the 12 V native system there’s lots of components like cell phone chargers etc. to be had inexpensively for quality pieces to meet your needs – never mind the plethora of 12V lighting options in LED.
You may say you don’t need a 2000 water inverter and that is probably true. However, having the availability to run a vacuum or have plenty of headroom for a coffee maker or whatever combined with the fact that halfway decent inexpensive 2000W psw inverters are readily available with 11W idle consumption up to say -26W for AIO stuff I’d just do it.
I’d suggest your 400W of solar should be adequate for you. Not overly sufficient, but adequate and possible depending on your batteries/type and expected loads. A 140Ah lfp battery will live under that acceptably re: charging capacity. Two 140Ah lithiums might want 600W of panels unless your daily Wh are fairly modest and you merely want a couple days of buffer. Each 200W of panels matches up adequately per 100Ah of usable battery storage.