What is the length and number of the parts of a conformational epitope?
I found this paper that analyzes 111 antigen-antibody x-ray crystal structures.

They find that in their dataset that "the large majority of Ag structures (86.5%) have CRS ranging from 20 to 229 aa." CRS stands for contact regions span which they define as "the minimum contiguous amino acid sequence containing all CRs of an Ag or Ab and represents the size of a complete structural epitope or paratope, inclusive of CR and the minimum set of supporting residues required for proper conformation." further on they mention that "The average and median CRS of all 111 Ag structures is 125 and 95 aa, respectively." and "the majority of the structures do indeed have epitope CRs that are clustered together in short, contiguous stretches ranging from 2 to 12 aa, longest contiguous sequence of CR being 5"

I hope this helps.