Looking to add some hair to our lime plaster, and received 9 hanks or bundles. The hair is around 3" long per strand should we cut this down say to half the length or use as is. Will be grateful for any advise.

Yup! And tease it out really well. It is an unbelievably frustrating job, aand almost makes buying pre-haired plaster worth it! In my experience, if you don't tease out almost to individual hairs you just get soggy clumps, however much you mix.