There are many ways to optimize gallery pages (optimize H tags, optimizing file size of images, adding short descriptions, good page titles, implementing proper tags on the image, good ux and so on). There is an excellent tutorial here. Good luck!

Organics around 15% and PPC about the same. Rough average comparing monthly totals average out compared to the summer months.

Yes, and it's fairly common. Each of the search engine may or many not use your meta title. If the search engine deemed that another title (derived from the laning page) will match the user's intent better, they may switch it.  Since Google & Bing have different algo's, this happens. For more info see How Does Bing Choose The Title For My Web Page.

I wouldn't change a bit. I always focus on making sure a site is accessible and has an optimal site architecture first. For on-page content, I will create (or attempt to create)  a compelling user experience by offering content that helps solve an issue the prospect may have and focus on optimizing conversion. Most people underestimate how difficult and resource intensive this is to do because it takes a ton of time involved with data gathering, analysis and creating the content. So after you are 80% happy with this (because that last 20% will take as long as that 80%), begin implementing your off-page strategies and work in conjunction with a continual effort on improving and adding on-page content. A core objective is focusing on great content and earning the links, so that is why I typically start there. As you know, this is a process that never ends. Good luck!

For Google, typically between 920 and 923 pixels (or roughly 160 characters).  However, this does change periodically.

We have been using MacRae's for a number of years and it returns a positive ROI. It's a good quality directory and we use it for industrial B2B advertising (we also use ThomasNet as well).  Others include: MFG.com/Globalspec.com/Alibaba (however--we don't use these anymore).

Yes, for the most part. Google wants to deliver the best results for visitors based on their search query. So if something is hidden from initial view this would impact ux and especially if it's poorly implemented (not intuitive). As you know, original and compelling copy is the best. Unfortunately in many situations, such as a large ecommerce site, it is resource intensive. It's best to avoid thin content. However, it does get ranked as you can grab a snippet and place in Google and look at the results. So yes, it's possible that Google will rank these pages with duplicate content in a hidden view.

I would advise you to tell your client to remove any hidden content and rewrite product descriptions. Depending on resources, they may/may not want to do this. If they don't, at least you made a recommendation. Good luck!

I don't think heavily. As long as the prospect can find the form easily (via menu item or small graphic), I wouldn't include one as it will take up too much valuable real estate on the home page.

Do you have access to the httpd main server config file? If so, please read Apache HTTP Server Tutorial: .htaccess files.

".htaccess files should be used in a case where the content providers need to make configuration changes to the server on a per-directory basis, but do not have root access on the server system. In the event that the server administrator is not willing to make frequent configuration changes, it might be desirable to permit individual users to make these changes in .htaccess files for themselves. This is particularly true, for example, in cases where ISPs are hosting multiple user sites on a single machine, and want their users to be able to alter their configuration.

However, in general, use of .htaccess files should be avoided when possible. Any configuration that you would consider putting in a .htaccess file, can just as effectively be made in a <directory>section in your main server configuration file."</directory>