Here's my opinion... If you are planning to use a pressure-washer, then just make sure you point it down on the engine (i.e. not from the side). This will keep water from working into things so much. If you use a hose, try this also, but it isn't quite as important.
As far as covering, the only thing I cover is the distributor or coil-packs (your car will have one or the other, not both). In the picture of your car, there are four spark plug wires sticking out of the top of the engine. Follow them back until they plug into something. If it's a round cap, that's a distributor. Cover it. If it's two little cans, those are coil-packs. Cover them. I don't cover anything else. An OHC engine will have spark plugs on the top (like your car) and they have boots that seal to the valve cover pretty well (and an OHV engine will have sideways plugs, so the water won't pool there anyway, and little pooling will roll out when the car moves). Just spray them carefully and you shouldn't have any water leaking by. Even if it did, it would evaporate when the engine heats up. It won't leak past the plugs into your engine or anything. Fuse boxes are sealed pretty well, and most electronics can handle some moisture. Just don't be aggressive in spraying anything electronic. That's my opinion. I've never had an engine not start after cleaning it (although I've only cleaned about 5 engines). However, it's up to you. The more you cover, the more you have to clean by hand. And for the most part, if something doesn't start it will once it's dried. But like I said, that's just my opinion.
I highlighted the spark plug wires in your photo in case you don't know what they are:
your engine
