Well the members before me have given to you good suggestions and I do agree with them. However, I feel that to start with if you can keep 5 cents per thread and 4 cents per post, it will be better. The activity on the forum will increase fast. Later on you can bring to 4 and 3 cents for thread and post respectively. Paypal would be most welcome payment processor.
Low payout to start with. If you can keep it 3$ to start with (say for first 10 requests or so) it would be excellant. That will earn a reputation of PAYING forum as many new members ask "Show the payment proof".