I personally prefer the fan to be at full extension but with the feathers still overlapping such that there are no gaps. That is usually at about 180 degrees, but may vary slightly either way. I always leave the first couple of layers of iridescent rump feathers attached to the fan and spread them evenly such that they cover the lower fan quills. That makes a much more attractive fan mount.
Here's the process I use with tail fans: I clean everything off thoroughly around the quills while leaving the connective tissue intact. I then borax the base thoroughly. I then take a piece of cardboard bigger than, or close to, the size of the fan, spread the fan to the shape I want, and then pin the fan feathers individually by running a thin "bobby" pin through the center of the fan feathers, spacing the feathers the way I want them, space the rump feathers evenly, and groom everything as needed. I then let the fan dry for a couple of weeks. After that time period, the fan is set and the pins and cardboard can be removed. The total amount of time involved for the entire process is an hour or two max.
In the climate I live in (dry, low humidity), nothing further is needed to be done as far as the fan goes. I generally add a wood base to cover the fan base, add the beard and spurs as desired, and it's done. Other than inspecting once in a while to ensure bugs or moths have not invaded, and treating for those if needed, nothing else needs to be done and the display will last indefinitely.