Awesome project! i see there is a lot of debating about wether answers should be free... how about making it optional? so you have both pay to see answers and answers that are visible without paywall? The free answers could be monetized with tips based on value4value. This way you could figure out which feature is liked more by the users in a more market research style.

another option would be for the author to set a price, but give the reader the option to refund a percentage based on how much value he got from the answer. if he got full value 0% refund, if he got no value 100% refund. you could then make the voting system based on this value system.