The fact that Cypripedium segawai is a rare species in its home in Taiwan really does not come into this equation as it is being mass produced on the continent and sold by just about every nursery involved in selling Cypripediums. I suspect the expensive price tag is at least partly because it is a difficult plant to grow, not according to me, but according to the Frosch website, which makes me even more convinced that your decision to start with species, and by the sound of it some of the more difficult ones, rather than learning the ropes on hybrids is the root of your problems.
How did the perlite get so sodden last October? I doubt that York's climate is so very different to my own, but if it is exceptionally wet then the thing about pots is that they can be put somewhere sheltered. By Lincolnshire standards we have had a monsoon overnight, water butts are full and overflowing, but I doubt that the perlite in any of my pots could be described as sodden because it is so free draining and because all stand in the shelter of the house. I have no reason to doubt Neil's figure of 225 mls of water per litre but to achieve this figure I suspect that I would have to put the perlite in a jug and leave it some time to fully absorb the water. This should not be happening in a plant pot. When I water my plants it seems as if the water is pouring out of the bottom of the pots as fast as I put it in. To get it anywhere near sodden I would have to block all the holes in the base.
My advice is to you is the same as I'd give to anyone new to Cypripediums or struggling with them, go buy an Ulla Silkens or a Hank Small.