Guido,
Two questions:
1) What's the most number of females you've put with a male? I don't think the male would wear out. The breeding season, the natural breeding season that is, lasts but a few days. Then he's got the other 360 days to recuperate. A male would never lock with 20 females, but providing an ample supply affords him the opportunity to seek out the most receptive (via pheromones).
2) In regards to the email: "mates should be same size" how is this possible? I'm of the understanding that a sexually mature female is ~2x the size of a sexually mature male. Looking at the OP's photos of the male, leucistic, hypomelanistic T. e. vagrans, could a female the "same size" be fertile? I would simple use a divider in the enclosure, mesh, plexiglass with scent holes, etc, to first determine the behavior/intentions of the pair.