I see that there is something wrong with the water profile that Seattle published. A check of the cation/anion balance shows that there is something wrong. I reviewed the published Seattle water profile and was finally able to decipher where the error is. It turns out that the City reports the calcium content (as CaCO3). The actual calcium content (reported as Ca) is about 8 ppm. That does make the cations and anions balance.
That is one of the benefits of using a water program that actually helps you learn about water chemistry. Bru'n Water has the guidance and calculators needed to better assess what your water report says and how to better adjust it. Those other programs are quite effective at telling you how much mineral to add to reach a certain ion content, but they sometimes miss the mark on giving you the ability to figure out if that mineral addition is OK. Thus the reason you are asking for advice. Download Bru'n Water and you will give yourself the knowledge to assess water adjustments. Bru'n Water includes a very substantial section on Water Knowledge to help you understand what you're doing and why.
The baking soda addition is large, but it doesn't push the sodium concentration too high. So that 4.5 g addition to the mash isn't bad, but it may not be the best way to go. The chalk addition is a waste of time. Experiments by both AJ Delange and Kai Troester have confirmed that chalk DOES NOT dissolve effectively in the mash and cannot be relied on to provide the intended alkalinity.
I also note that you're planning on adding the chalk and baking soda to the sparge water. Sparge water should NEVER have its alkalinity increased. Sparge water alkalinity must be low to moderate and the pH should be between 5.5 and 6.0. Acid is typically added to the sparge water for ALL mash grist (both light and dark colored) to reduce the potential for tannin extraction. Keeping the sparge water temp below 170F is also important.
As noted above, the calcium content of this water is very low. It should be brought to above 50 ppm for good fermentation performance. In addition, the magnesium content needs a very slight bump to about 5 ppm to again improve fermentation performance. The sulfate and chloride concentrations are nice and low and you will have plenty of latitude to adjust these ions to create the profile you desire. Now, a better way to add alkalinity and calcium is to use pickling lime. Pickling lime is completely soluble in water, unlike chalk. Bru'n Water has the calculator to tell you how much to add to your water to produce the desired alkalinity and calcium content.
Glad to hear that you're concerned with the plethora of brewing water programs out there. But instead of 'oh my god', next time I suggest you write OMG (One More Guinness). ;-)
To those of you that have not taken a look at Bru'n Water, I invite you to take a test drive. There is a much better way to assess and adjust your water. Yes there is a lot of information and capability in there, but you'll have the ability to brew better after you figure it out.