The sercice I have been most impressed with is this: http://www.removeem.com

However, there was a recent moz post about this exact issue: http://moz.com/blog/google-disavow-tool

I hope that helps.

Answer to your first question.  Yes plural and singular count as two different keywords.  However, if you implement the plural form of the keyword you will also be using the singular form of the keyword, as normally the plural of a keywords just means to add an "S" (i.e. Best Developer and Best Developers are considered two different keywords but the plural of the keyword still exists within the phrase so it can end up counting as two different keywords).

In answer to your second question, these different keywords may have the same global monthly search but the priority in search ranking will go to the one that matches the search query the closest.  So if you have "photo booth props" and "props for a photo booth" but someone is searching for "props with photo booth", the person who has that exact match will normally rank higher than the previous two keywords associated with your site.  However, there are exceptions, such as a site that has major authority on photo booths might rank for the keywords solely based on authority.

I hope this helps.

Agreed

Here is a tool to find out how many out going links are in a website:

http://www.getrank.org/tools/link-extractor/

also if you have the seo quake tool in your browser it will tell you how many outgoing links are on the page you are looking at.

The sercice I have been most impressed with is this: http://www.removeem.com

However, there was a recent moz post about this exact issue: http://moz.com/blog/google-disavow-tool

I hope that helps.