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
What I meant is it is better than spending huge amounts for banner advertising on bitcointalk.
You should make a post at least 50 post per month. 0.2 per month just for 20 post is high rate, even if you rank hero member.
I think you need make a rules which your advertising is can be more exposure.