Pretty straight forward task, im guessing you want to use the pi as the access point, i can program your needs, provide you with custom image with everything setup, which you write to the pi's sd card plug in ethernet for internet and people will be able to access internet after liking the page, that is they will log into pi's wifi ( log into thier facebook account, my program will check if the user has liked your page or not and give internet access) once the user connects to the wifi he will be prompted to login to facebook and like the page as well. feel free to check my profile for past projects and reviews.