The whip antenna at the masthead should be quite unobtrusive; If the mast is hollow and you can run the cable inside it should maintain the look and avoid any problems.
You can get a Windex wind indicator that fits over the antenna.
A passive radar reflector can be hoisted when on passage but with no spreaders it might be a challenge to keep it out of the way. Larry Pardey reckons that crinkled aluminium foil inside a wooden mast is a very effective radar reflector.