Can anyone give me an advice about schedule of buses going from Antalya to Kumluka / Kas and back? Especially in December (if it is different in off-season)
For Kumluca, based on this website, there are a lot of bus firms that you can use from Antalya (or to Antalya). Mostly used ones are Kamil Koç, Metro Turizm and Pamukkale Turizm. I choose one of these if I were you.
You can check their websites and see the bus schedules. These schedules usually won't change based on seasons by the way.