tree/plant coverage to boundary

Spritzhenry and others can give you specific plants/trees. I just wanted to address a mistake I made - planted deciduous trees for privacy, and in the Fall lost all privacy..... maybe go for evergreens. I resorted to trellis and vines - a lower profile against the house. If that is an option for you for a bottom story, it is fast and economical while other things grow.

18' is very tall and will cast a LOT of shade. You'd have to plant shade loving plants in your flowerbeds. Do you know if your soil is acid or alkaline? I would think about flowering shrubs to add interest: if your soil is acid, there are Camellias which grow quite tall (not 18' though) Pieris, larger Skimmias and Rhododendrons. There are lots of interesting conifers but I am concerned that they might be as bad as your late-lamented Leylandii in taking over. I reckon a trellis would be a good compromise with perhaps scented evergreen Loniceras on it. But you live there and only you know the situation.