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I don't see any reason why not to add alt text to the stock images on your website (I say this both as a site publisher and as a professional photographer).  The alt text doesn't imply ownership of the images, but rather it's designed to provide an assistive description as to what the image represents.  The only area where I think you would be deceptive is if your alt text claims something that is blatantly false, such as showing a stock image of a man and the alt text indicating that it's a photo of your CEO.

Descriptive alt text, including keywords, will have a positive effect on SEO.

The All in One SEO Pack plugin is pretty good and used quite widely among WordPress-based websites.  It focuses on on-site optimization including keywords/density, appropriate linking, canonical URLs, and the like.

Use of this plugin should not cause a 40% drop in traffic (you didn't say what you mean by a "dip", but I assume you mean traffic or search traffic).

Such a significant drop in traffic after the Penguin update is more likely to be related to what Google is perceiving as non-organic backlinks, including paid links or link exchanges.  If you engaged in such practices, it would be best to work on removing those backlinks, including the link disavowal tool if you can't have them removed.

Seems subjective to me; I would make the call based on whether you're really tracking multiple campaigns or one.  Are all of the keywords related to a single core business or marketing plan?  Keep it together.  But if you have distinct businesses or major product areas that happen to live under a single domain, those would be good candidates to be broken up into separate campaigns here.

As someone who receives pitches for guest posts, here are the two distinct reactions that came to mind when I read this:

• It doesn't bother me that someone else is doing the outreach, as long as they're representing things correctly.  I've received pitches along the lines of "I'm contacting you on behalf of..." and it doesn't bug me at all.
• It seems really weird that an expert wouldn't use their real name.  Expertise is very closely linked with credibility, and I can't help but wonder "what do they have to hide?"  The exception here is if this person grained their expertise while doing business or otherwise acting under a pseudonym... it's not that one can't become an expert without their real name, but it's the fact that if they became recognized as an expert using their real name, the shift to using a different name seems funky.

Having worked quite a bit with WordPress (since version 1.2) I can't think of an SEO reason why this would cause a problem.

The only potential gotcha that comes to mind is that I'm not sure how well WordPress' one-click updater feature is going to work when WP has been spread amongst multiple directories.

I once ran into a similar situation with a new website with a domain I'd purchased.  Turns out that a previous owner of the domain had apparently been doing problematic things.

I submitted a reinclusion request to Google, indicated that this was a new domain, provided evidence of a few legitimate backlinks, and asked if they could look into the matter.

Within a few days, I was included in search results.

Forgive me if I've overlooked something obvious, but how can I exclude a subdomain from a campaign?  I want to crawl/analyze mywebsite.com, but not subdomain.mywebsite.com

Thanks in advance...