Droste,
If you choose to do the MEI/CFI as your first one you will have a MEI rating, and a CFI rating, only valid on multi engine aircraft. You could not teach on singles.
As for the poster that asked about the CFI being revoked if his candidate fails??
Each CFI has a training record of passes and fails. If he/she should get too many fails, or a very bad fail, he can be asked to the FSDO for a talk (councelling) or could be re-examined under the 44709 rule, to check his ability. It is in the rules, but rarely used.
Speedbird 48.