You're basically looking at a system very much like what recreational vehicles use.
So, from that standpoint, most of the details have been worked out for years.
The downside is, like marine parts, RV parts tend to carry a premium for what they are.
I have, however, found that many of the same parts sold for mobile home use are nearly identical and often cheaper than the RV specific alternatives.
We have a small travel trailer on a remote piece of land in rural WV. I bought a 40 gallon water tank (about $100, on ebay) and put it on my little trailer. The camper has a 30 gallon internal tank. I use a cheap Harbor Freight 12v pump to transfer the water between the two.
The camper has a small hot water heater. About six gallons, IIRC. The one we have runs on either 110VAC or propane. Heats up pretty quick. Tankless, on demand water heaters were pretty new and pricey when I built our camper, but they may be a better option now.
RV shower heads almost always have a shutoff valve. You really have to take "Navy showers" where you wet up, soap up, then rinse off rather than running the water continuously. If you don't, you'll run through all your water in a very short time.
If you want to store/move a lot of water inexpensively, look into IBC tote tanks. They're around 250-300 gallons and can usually be picked up used for $100-150. They're caged and used for bulk storage of industrial liquids, but those liquids include food processing. If you get one used for something like fruit syrups, then it can be used for potable water. They have the footprint of a pallet and are about chest/shoulder high.
