I like the way you drew the roof over the garage in your sketch, too. It gives me a better perspective of the proportions. The only thing I'm still wondering about is with the new roof right next to the main body of the house, it's quite a long line of the same roof. My first thought was a dormer on the addition, which I think would look good, but you made the point earlier that front door is on the other side of the house, and not wanting to compete with that, so I go back and forth. And I don't know about the middle of the house sandwiched between two peaks. Maybe there's a way with landscaping, or by adding something to the facade of the middle of the house, that would give the middle a little more dimension and break up the long lines? Although, sometimes it seems the better approach is to go with the horizontal lines and build on them, in which case the windows in the middle would look less split level and better proportioned to the length of the whole house if they were wider.

Snap a photo on a sunny day then use the Sherwin Williams ColorSnap app to play with the colors. I would select a tone slightly darker than your mortar for the garage door and a color slightly darker than your darkest brick for the front door. I would then on the garage door install magnetic faux hinges and windows; this will add detail to the door, like the below house. I know they can be found on Amazon, not sure where else. Before: After:

There are 4 photos you show- but I only gave 3 paints. So just wondering what the last option is?

While it will shrink your side yard, you might consider planting a couple of rows of cedar trees or other evergreen trees or shrubs )that keep their leaves year round) to create a "green fence" between the railroad track and your home. Not sure it would help with the sound but it certainly wouldn't hurt. After you plant the first row, plant the second row with those trees/shrubs blocking the view of any space between that first row.