In April around 12 years ago I bought a P. vietnamense on an orchid exhibition in the Palmengarten in Frankfurt Germany. The plant was, with several other species (mostly without label), that all were in bad condition (damaged leaves, no flowers or buds) on a bargain bin. As I saw the broad leaves I was convinced to know what it was. Costing only ten Euros, the plant was very cheap, so I took the risk. At home I planted it in a mixture of coarse pumice, charcoal and bark and placed it on the windowsill (southwest exposition northern hemisphere) next to my other plants. A new grow emerged three to four months later. Around two years later, the plant flowered for the first time. Since then, this plants flowers regularly around every two years (two years ago with three flowers, this year with one flower). I have transplanted it only twice in the meantime, always in the same mixture. Since then, this plant produced several capsules (mostly hybrid pollination).
I have sown these seeds on a coarse mixture of pumice and pine bark, that I first sterilized in zip log freezer bags (in the microwave), then infected with soil particles from other pots where orchids germinate, after some months of resting to let the fungus develop its mycelium. It usually does not work with all bags, but with my restricted space, I get enough seedlings. They can stay in the bag for around two to three years.
In my personal experience the species is not difficult at all. As I have experienced so often, the main problem in successful culture of Paphiopedilum is to eradicate pests like Tenuipalpus pacificus and Brevipalpus spp. These mites are present in so many professional cultures where they are held down so that they cause only minor damage. When such a plant comes into a new culture (especially where the air is drier), these pests explode and destroy. Because of that, every new plant in my culture is put into a sealed bag, poisoned and stays there for at least four months.
All the best,