Keywords General - All in One SEO Pack Forum

I have 3 questions for you.

1.  I am rather new to building websites /webdesign and am using WordPress with the All in One SEO tool.  I would like a general rule of thumb as to how many key words to add.  I am only using words found in my blog or page but recently I have learned there is a term called key word stuffing.  Where do you begin to cross the line- how many is too many?

2.  We will be opening up a job resource widgit on my website with a page for every state with a Google custom search box on it. I have customised the search box with key words as  directed by Google Adsence.  If I also use the key words in the SEO plugin - jobs or New York jobs etc. on that page and then Ohio jobs on the Ohio page…is that considered key word stuffing because I have 50+ pages with similiar SEO key words- the difference is the state name? 

3.  Have you any experience with how to incorporate the Google Adsence for search custom engine?  How does one describe how to use the custom search box to my users without using the same terms you built it with - which also will be the SEO keywords I would use.  Should I not put key words into the SEO tool on these pages? I am not sure how to proceed.  I have not made the pages public yet.  

The plugin is excellant- thank you for building it by the way.