A range of spacing could be appropriate, depending on what your goals for the tree are (nut production, timber, specimen tree, etc). Because of the nature of black walnuts (lower branch drop) and because of the thousand cankers disease (which will probably be in your area soon), I would recommend not planting it near any structure. And, yes, 8 hours of sun should be sufficient for a healthy tree. Below is a link that I hope will be helpful in your project.

Here is a link that might be useful: Planting a Tree or Shrub

Probably a minimum of 25-30 feet apart, 40 would be better.

Thanks guys, trees are planted, now to sit back & enjoy.