I would keep it simple, choose a lens in the middle range for 4x5, as you might choose a 'standard' lens if buying a first 35mm camera. So a 150mm is around 45mm equivalent in 35mm. That can be your datum point and work out either side from there when you buy more lenses. I find a 90mm, 150mm, and 240mm an ideal range for the English landscape, and it would be good for architecture as well. But the 150mm is the 'do-it-all' lens if I can use my feet to zoom.

Prices for a 150mm Symmar S are very good at the moment, with plenty about. The filter size isn't outrageous at 58mm and it gives tons of coverage to allow for movements.