Best Approach? | Wordpress MultiSite -or- Simple Sidebars/Menus/Etc

[ItsPhipps]

Ok, I want to get started on a new project, but I want to start off on the right foot from the start. So here's what I want to accomplish.

I want to start a network of sites that are city specific. There will first be a main site that is just general, and a network of city specific sites underneath that.

The main site will contain all the information that stays the same regardless of location. It'll have all the cornerstone content type of stuff. The city specific sites will have all the same cornerstone content with the city name inserted, plus extra content that is specific only to that city like local events, local news, etc.

Now I know that I can achieve this with either Wordpress MultiSite, or by using the awesome plugins and capabilities that Genesis comes with. I know that I could use nested categories, simple sidebars, simple menus, and change CSS based on category to do exactly what I want with Genesis.

Kind of like this:

Main Site
–Los Angeles Site Category (with its own header, sidebars, nav)
–––Los Angeles Site Sub Category 1
–––Los Angeles Site Sub Category 2
–Denver Site Category (with its own header, sidebars, nav)
–––Denver Site Sub Category 1
–––Denver Site Sub Category 2

It seems like using the Genesis capabilities would be the way to go due to simplicity. The main question, or concern, comes with the cornerstone content. I'm not really sure how to execute that.

I want all the cornerstone content to get copied to each "city site" with the city name inserted into it. For example:

Main site- How to make the grass greener in your area.
Baby site 1- How to make the grass greener in Los Angeles.
Baby site 2- How to make the grass greener in Denver.
Etc....

It seems like MultiSite would be the best way to accomplish this since I can push an article across all the baby sites and use a shortcode to pick up the city name. I'm not sure if I can do this with categories though or how that would work with an SEO aspect. The only way that I can think of would be to create a new article for each category and manually add the city name to each one.

Here are my questions:

-It there a better way to do this that I'm in the dark about?
-Would having duplicate content–with different city names–be good or bad for SEO on a site?
-Is there a way to do this using categories without having to post multiple city specific articles (cornerstone content) at a time?