I keep mine seperate, too- mostly because they have different growth habits. Some are viney and some grow so fast and others have short internode lengths. I am kind of intrigued by the idea of mixing them but for me there would have to be a concept- ie. all same bloom time or something.
I have been collecting, studying and selling hoyas for about 10 years. This Cubit is about growing hoyas, and about the hoyas I have to sell. I welcome any and all hoya lovers, whether you want to buy or not. Hooked on Hoyas is another great Hoya sight