Well the thing is, just like Places violations, you can get away with multi NAP on the site and many people do. It's just that if it goes south and YOUR listing is the one that ends up with a big ClusterF merge, then it's a big pain and hours of extra work.
In addition to the potential merge problem the other issue that can come up with mixed NAP is location confusion. If all locations are on home page or in footer on all pages and if all G+ L pages link to home - then Google can sometimes get confused and just drops you out of the pack.
So best practice to try to avoid merges and getting dropped from the pack is no mixed NAP.
As far as HOW to set it up, it kind of depends on the situation, as there are so many variables.
BUT to rank well in local you NEED local NAP. SO one of locations ideally should be prominent.
And the home page is most important AND the easiest to rank. So ideally you optimize home page for more important location OR location in biggest city that's hardest to rank.
EASY EXAMPLE: Main office in the big competitive city, 2 branch offices in smaller cities. You'd optimize home, footer and contact for the main office that's in the hard to rank big city. At top of page and on contact us you'd make the other locations REALLY CLEAR for customers. And in footer too, links to our other locations.
We have 3 Locations to Serve you. Click the location that's most convenient:
New York, Philadelphia, Boston
So then Home and contact us would be optimized for NYC with links to the other 2 location pages which would be optimized as I explain further down.
HARDER EXAMPLE: Let's say it's a Dentist. 3 offices ALL same city. ALL equal in importance.
A) They are all competing with each other in the rankings and likely only one may rank on page 1.
B) Only 1 can be on home and footer and that's likely the one that will rank highest, or at least will be the easiest to rank.
So in the 2nd scenario they just have to pick one to be most prominent in Google. And the easiest to rank also MAY be the oldest location. So I'd ask Qs to try to figure out the best one to optimize as sort of the main office on home, footer and contact us. But then make the other locations super prominent in a graphic at the top and on every page. "Click here for our downtown office, here for Northend, here for south end."
But then there are all kinds of examples that are different than the 2 above.
Then as far as the link on the G+ L page and the location pages, I would link each G+ L page to the location page on the site.
HOWEVER keep in mind that organic ranking rules so that page would need to be optimized for city and keywords too in order to rank. So would need to be a location page with NAP for that location and a map PLUS KEYWORD CONTENT and services offered.
So each location page needs to be like a combo home page and contact us page.
BUT each page must have unique content. Can't just be duplicate content with city changed.
If I remember right Roto-rooter does a decent job with location pages and they usually rank pretty high. Have not looked at them for awhile and I think they have tried different strategies and some location pages were better than others. So I'd search plumber in a few cities and find some that rank #1 and look at them.
Here are some other posts that may help:
http://localsearchforum.catalystema...ges-local-search.html?highlight=landing+pages
http://localsearchforum.catalystema...er-local-landing-pages-yellow-brick-road.html
http://localsearchforum.catalystema...ine-optimization-strategy-multi-location.html
http://localsearchforum.catalystema...ation-franchise-common-corporate-website.html