CFI and Ground Instruct
 

Is it neccesary to have a Ground Instructor Certificate to act as a CFI?

Negative...

61.183 lists the requirements.

Nope. FI > GI, so there's no benefit to doing both of them.

You might think about taking the AGI written test. I believe you need it to get your gold seal.

AGI or IGI to earn Gold Seal. I went the IGI route.

Also, the ground instructor doesn't expire like the CFI does.

Same story with me...got my IGI so I could add the Gold Seal..and yes, your ground instructor certs never expire...for whatever reason.

AND I'll second that having a CFI or II or MEI and no AGI/IGI is good enough to teach your students both in the air and the requisite ground knowledge.

Good question though. :)

Except you will get out of doing the FOI oral portion on your checkride :p

Don't count on it - certainly not at the Richmond FSDO.