In my limited experience the biggest limiting factor is where your engine gets it's air.

If your intake sucks up water the engine, at the very least, stops. Unless your fast turning it off and very lucky it's toast. If there is any chance of it having sucked up water you need to pull the spark plugs and clear the cylinders before you do anything else. Some trucks and SUVs suck air through a hose that reaches down in front of the wheel well. Which means if the water gets much above the hubs your sunk. Simply relocating the air intake so it draws higher up can make a big difference.

In my experience the wiring isn't usually all that vulnerable. Fresh water isn't all that good a conductor and because the engine compartment tends to get pretty wet anyway they are protected from shorting out fairly well. I would look at where the battery is. You don't want water to get into the battery or let the terminals short out. A sealed battery and/or moving the battery shelf up some might help. A plastic battery box might help keep splashes at bay but if you can't keep the water out you need to provide a drain for it to get out.

This is also true for tail lights and position lights. If they are truly sealed your good to go. But if not they have to have a way to drain. Using silicone dielectric grease, designed for the purpose, to keep water out of the sockets and prevent corrosion is a good idea.

Spark plug wiring are typically sealed under rubber boots with silicone dielectric grease. If your planning to ford streams you would be wise to closely inspect those spark plug wires to make sure thee are no cracks or worn spots. Intact and well sealed they shouldn't give you any trouble.

Of course a diesel would eliminate the spark plug wires as a source of potential trouble.

I'm not real clear on the effects of fording on wheel bearings. I have heard that for just occasional crossing of water over the hubs there is no need to change anything. Just make sure they get regular maintenance.

This is what I have done and so far so good. A couple of times a year I was running a small car deep enough to have water over the hubs during hurricane season. A friend who does a lot of fording streams with a jeep suggested I might switch to a special grease and maybe install some sort of bearing protector. The car kept rolling so I guess everything was okay and now I have a truck. Still something you might ask your mechanic about.

As long as you exhaust system is intact the air pressure of the exhaust gasses should keep the water out. At least well enough for short dunkings.

You might ask around to see if there are any off-road or FWD clubs around your area. They would have experience in your area and be able to look over your vehicle with a critical eye.