I am developing my basement to include a bathroom that will be on the
front side of the house. What is the minimum diameter of the vent
for the exhaust fan I can get away with that would make the vent
outlet look good? Or perhaps the question is is there an attractive
vent outlet cover I can use for the regular 4 inch vent.?

Assuming we're talking plumbing vent,
would a Studor vent or
air admittance device
would work.
TB