When requesting links from other sites what percentage would be considered good for accepted link request?
I don't think anyone could say what is a good percentage..in some niche, people freely give out links, in others they don't. Rather then send a mass request, try and build relationships within your niche and then send out requests. People will be more receptive.
entirely depends on your niche and nature of the site. if it is a commercial site selling products, you will have less luck and if it is non-commercial resource site then you will have more success rate. also depends on whether you are asking for one way link or link exchange
It may depend also on the nature of your comunication to the webmaster ... Try gentle speaking, dont start making requests and that kind of stuph .