1) No. The foliage will vary considerably between the different species and hybrids.
2) This question is best answered with respect to your specific location. In my climate all hellebores do very well - in colder climates, some species are of questionable hardiness or tend to dieback completely in winter, precluding their ability to flower.
3) Depends a lot on the quality of the nursery and where it is. I sold 32 different varieties at my nursery this season. But, in all fairness, x hybridus forms tend to be the most widely offered - the Sunshine strain is only one of many of these.
4) Yes, there are double flowering forms of x hybridus. IMO, they tend to be less vigorous and not as freely flowering as the singles and come in a narrower range of colors.

thank you so much for your help..I appreciate it alot
karen