Half of my collection are roths, most of the crosses come from Taiwan.
Roths are not difficult at all, they are actually pretty easy if you get a modern clone. The older crosses or collected plants are much more difficult. I do not own one of those plants tough.
This is my biggest roth: '266'x'J' --> It is a cross from Taiwan. 266 is 'Mont Millais' x 'Val' and I was said that "J" stands for "Jeanet". I am not sure tough.
As for the potting mix: they like a mix of seedling bark, CHC and Coco fibre and some sphagnum moss. I get good results using coconut fibre in my mix. Some of my roths are in pure CHC and they do fine too, but I will use the above mix the next repotting as it is the one that turned my 266xJ into a monster.
Roths usually do better when you dont give them too much light. In the net there is a very good PDF from Xavier Garreau ("roth" on ST) about roth cuture. Just google it.
Always keep them warm all year round with a slight temperature drop in winter and don't give them too much fertilizer.
I am growing under lights btw.
Feel free to ask questions..