Hi bazard,
7foot is rather small for any kind of nut tree that I can think of. The corkscrew hazel is slow growing and will eventually reach about 10 foot after many years but sadly wont produce the good crops of nuts that you want, otherwise you could try a purple hazel (Corylus avellana 'Purpurea') and grow it as a coppice and cut it down to the ground every few years, even the nut's they produce have a purple tint as well as the leaves.
Male and female flowers are produced on the same tree with hazel's so pollination should'nt be a problem.
Mulberry get pretty big too approx 20ft but some of the standard flowering crabs may be suitable, the variety 'Golden Hornet' will catch the eye from a long way off. Good Luck. Tbird+