I dont know about WF but about DP:
1) to post in the B/S/T section you should hav a min of 25 posts and a 15 days account min. As for sales, people there normally care only about reviews. There are some very reputed members there like getjimmy and a good review will mean a gazillion sales even if your rep is zero. Get atleast 2 50+ itraders to write good things about your method and you will do well.
2) It would be best to stagger your pricing. First 5 copies for $10, next 5 for 15 and the rest for 20 or something similar(adds a sense of urgency and also gives the buyer a feeling that the product is nominally priced). I wouldn't suggest crossing $25 unless you are confident of getting some really glittering reviews.
3) PAYPAL, hands down. Some(very few) might ask for WM or LR payment so might want to keep those options open if you dont want to miss out on 5 more customers.
4) Depends on too many factors. I would say a good method(=good reviews) priced at 20 might sell anywhere b/w 30 to 50 copies