How could I run this giveaway?

[mchll9898]

Hi, I'd like to do monthly giveaways on my forum.

Each post = 1 entry. And then at the end of the month, a random winner would be chosen.

To prevent abuse I'd like to be able to:
1. limit qualifying posts to specific boards
2. have a minimum number of characters for a post to qualify (not absolutely necessary if this is too difficult to do)
3. limit to a specific usergroup

It would be great if I could somehow set a date range, then generate a numbered list of posts that fit the criteria above and then I could just use random.org to choose one. Is there a way I could gather this data?