these MODs will only affect posts already made. If you allow guest posting, then you are shooting yourself in the foot before you start.
If you do not allow guest posting, then spam posts are usually not a problem.
You need to disallow guest posting anywhere, then install one or more of the spam MODs found here:
that will take care of about 99% of spam, then your approval MOD will let you decide what posts made by your members are appropriate and which ones are not.