I think this van has 4x4 rather than 4wd. Yes our Toyota Hiace also says 4wd, but it is actually more 4x4, and I think this one will have (literally) the same transfercase as ours.
So that means there should be a 4x4/4wd button somewhere, and I already see the low-gearing stick.
Ours has the 2L engine, this is the 2C. These oldskool diesel engines are very reliable, especially without turbo. But it also means they are very noisy, and not very powerful.
That didn't stop ours from going over all kinds of terrain, because it has low-gearing. I've driven over all kinds of stuff including soft sand. It did great.
When back on tarmac and having a highway or other road with higher speeds going up the mountain, you will be annoyed by the lack of power and your speed is going down.
This TownAce has even a smaller engine, and I would like to know how much it weighs. Also, if you are going to add lots of stuff (as you are talking about storage) it won't be great.
You should have a realistic idea about how fast you want to drive on the highway and how long you want to drive, because the engine noise can become annoying.
This one is looking really nice, and the price is not even that strange if you look at the Japanese market for campervans.
But if you would just take a normal van, for example a 4x4 van from Toyota or Mitsubishi, from that time, the price is a lot less.
I would think that in the US you could get a (converted?) 4x4 van for less, and build something in there.