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Local SEO is a different animal than organic SEO, but organic signals have played a much bigger part since the Pigeon update. External factors that affect your rankings in the local pack include business citations and reviews. Check out the 2014 Local Search Ranking Factors. Backlinks do have an effect on local search but probably not as much as they do on organic search.

Below are some great resources for local SEO:

• Mike Blumenthal
• David Mihm
• Andrew Shotland
• Phil Rosek 
• Local Search Forum (Linda Buquet)
• Whitespark (Darren Shaw, Nyagoslav Zhekov, et. al.)
• BrightLocal (Myles Anderson)

With all of those parameters, it's doubtful that your site is being crawled efficiently.  In other words, the Googlebot gives up before it has a chance to crawl all of your pages. You should be able to configure URL parameters in Google Webmaster Tools to let Google know how to handle each parameter. This presentation breaks it down.

I've never heard of Google using class names as a ranking factor, and I can't see any reason why they would. It would be easy to manipulate, and class names don't affect the user experience at all.

My takeaway from the webmaster guidelines you referenced is that user experience is an important ranking factor (something we knew already), and Google needs to access the page's Javascript and CSS in order to evaluate the user's experience of that page. Google wants to render your page in the same way the user experiences it for indexing purposes. That's why they threaten to penalize your site if you disallow crawling of Javascript or CSS.

Assuming the plumber provides services at his customer's address, it would be considered a service area business (SAB). Consequently, you would need to add it to Google My Business with the "I serve customers at my business address" option.

While it's much more challenging to get an SAB in the local pack, there's a lot that can be done to improve organic performance for location-based queries.  Assuming you've covered your bases with on-page optimization, you'll want to focus on content and off-page optimization.

Add content with a local focus:

• Does the plumber belong to any local organizations like the chamber of commerce? Be sure to include those on the website.
• Is he active in any local charities or fundraising events? Include those in his bio.
• Are there any local laws or regulations that you can add content about on the site?
• Add case studies or testimonials that includes location-based content.
• Is there a way to add photos from the target city?

Off-page

• Try to get links from websites with a local focus in your area, including the local organizations, charities, etc mentioned above. Some old-fashioned local PR will help.
• There are quite a few local search directories that do not require a visible address.
• Develop a process to encourage customer reviews.

Mike Blumenthal posted a breakdown of a Mediative study in September that you might find useful.

LOCAL HEAT MAPS – LOTS OF ATTENTION, NOT SO MUCH CLICKING

What makes you think it might be a theme issue? Both the Moz toolbar and the Screaming Frog tool show the title as "Yoga Übungen - Mit visuellen Guides, Videos & viel Inspiration," so I would be very surprised if Google was reading a different title from the page.

Matt Cutts did a video about what criteria they use to change page titles back in March, and Jennifer Slegg posted a breakdown at http://searchenginewatch.com/sew/news/2342232/why-google-changes-your-titles-in-search-results.

Cutts mentioned 3 criteria that they use. If your existing title doesn't meet that criteria, they may change it.

1. Concise (short enough title)

2. Good description of page and site that the page is on

3. Relevant to your query

Apparently, Google finds it more relevant to put the Category name + the name of your site.

watch?v=L3HX_8BAhB4