Fuel Hoses
Your fuel system is pressurized, meaning you have a pump that pulls fuel from the tank runs it to the engine and then it goes back to the tank, so fuel is continuously flowing in the fuel system while the pump is running. If you rig up a temporary system using a portable fuel tank you need to make sure the return line is going back into the tank or you could have a fuel spill or empty the small tank pretty quickly. I'd use a portable gas tank with the fule pickup line going to the racor and the engine return line going back into the tank through the cap. A gallon of fuel will run your engine at idle for an hour or more so you don't need much fuel. Engines exposed to water happen all the time, reference your car every time it rains. But submersion is another story. Are you sure it was even submerged? If water didn't reach the air intake it may not have gotten into the cylinders. I certainly wouldn't want my alternator submerged so check that out for sure.
The coolant system is a closed pressurized system so I don't see any way water got in there even submerged. The white crystals you see may be calcium deposits but I doubt they are a concern. You can get some stuff at a auto store to flush your coolant system, why not try that then drain it and fill with antifreeze mixture. Of course the motor will have to run to let it circulate a bit to flush it.
As for the five gallon bucket raw water plan, I run my motor with the five gallon bucket in the cabin and just keep filling it with water when the bucket gets half empty. You have to stay and tend it but it's not a big deal. Works great for filling the raw water system with antifreeze for winterstorage. Just fill the bucket with the pink minus 50 stuff and suck it through the system. Actually you don'tneed five gallons for that a few will do.