1. The first and most important thing is contouring the slope away from the house. Have the ground built up at the foundation several inches, then grade out. It is also important to lay down heavy landscaping plastic and rock going out 3-4 feet. Most water issues are the result of water running directly down the foundation wall. The plastic and rock is critical because it forces the water out several feet away from the foundation. This step alone fixes most every problem.
Is this as simple as just laying down soil near the foundation walls and grading it to slope towards the yard? I am a bit unclear about the heavy landscaping plastic and rock you have mentioned. Can you clarify?
2. Down spouts are critical. Make sure the down spout extends past the rock, so it must go out 4-5 feet. The extensions are helpful but they have a tendency to come off in heavy rains. I like to have a solid 5 foot down spout with a cement water channel at the end.
There are downspouts in metal coming down from the gutter. What I have done is purchased 10 feet drain extension corrugated solid pipes of 4 inch diameter from Home Depot that I have attached to the bottom of the gutters to steer water away from the front and sides. If they have a tendency to come off, I can screw them to the end of the metal downspout. Is this sufficient or are you contemplating something different?
3. Watch what happens to your gutters in heavy rain. One common issue is gutters getting overwhelmed and water runs over them and down the foundation. One way to prevent this is increase the size of your down spouts to increase water flow.
Same as above. Can you clarify?
4. Install window well covers. Window wells are just rain catchers.
Ok. I will try to find some on Home depot
The deck is a major area of concern. I have had two situations where water came in under a deck that was on the ground like yours. In both cases the ground under the deck had a pocket by the foundation where water collected. The deck made it worse. I had to remove boards from the deck to add dirt, plastic and rock.
Personally, I don't even like decks that sit on the ground. I would rather build the ground up higher and have a poured cement patio. In your case, you can see the back yard slopes towards the back of the house. I can't see your entire back of the house, but it appears to me, you could build it up 8-10 inches at the foundation and have it slope back. I would rip out the deck and patio and build it up, then pour a nice stamped concrete patio. with good slope. The rain will run right off the patio and it will force the water 10+ feet away from your foundation. I know this could be costly, but right now your house is at the bottom of a hill, which is not good.
Ripping out the deck is a major endeavor and would most likely be more expensive than installing a complete internal french drain system. In addition to the steps I mentioned above, can I install internal french drains for the front of the house and back of the house (due to the aforementioned deck on top)? This way I can cut down the cost of french drain installation by 50% as now they would need to do only about 80 feet instead of 160 feet. The sides don't seem to have water and I only see minor efflorescence. My hope is that if I grade the sides, it should be sufficient. What are your thoughts?
If I do all the above, do I still need a shale before the water hits the deck? The shale would introduce an inconsistency / separation in the backyard, isn't it?