I don't have advice on cultivars, and live in a totally different zone, but I do have hazelnut and filbert bushes. There are filbert trees (usually called Turkish Hazelnuts), but there are also varieties that grow as a large shrub and others that grow as a small, compact shrub. If you went with one of the shrub varieties, you might be able to have either pecans or almonds and filberts. (I'm always trying to figure out how to squeeze one more thing in to the yard, so that would be the most appealing solution for me. ;))
My filberts aren't producing yet - this will only be their third season in the ground - so I don't know how well the cultivars I selected will produce, but I got them from Burnt Ridge Nursery, which has one of the largest selections I've seen. Their bareroot plants are very, very small, though and sometimes don't arrive with the best root system. I still order from them because the prices are good and I'm willing to take a chance, but you might want to go elsewhere if you want larger plants.
