Mike Schumann wrote:

How long of a runway do you need for an effective / safe winch and/or auto
tow launch environment?

I can only talk for winch launch. Safety is not a problem. The problem
is that you must have enough height above the winch to reach a thermal.
How much this is depends on your site.

E.g. at our field, we usually reach about 300-350 metres AGL. This is
usually not enough for us, with few exceptions. 100 metres more would do
it. So we are stuck to aerotow.

Stefan