1) Making a fixed campaign with 0.2 per month for 5 best quality posters, min requirement only 20 posts , so something like 0.01 per post.
I think that not a good idea, better you reqruit more people with low rate maybe 0.0007/post like bitmixer
It would not attract posters with excellent quality and encourage spam. If you were to attract spam posters, you would end up having lots of people with poor quality and it would pollute the forum and portray a bad image for your business. People would also start blocking those with your signature as it does nothing to contribute to the forum.