Ballpark around 600-800km, have done with more or less but I would recommend around there.
Assume you will need to qualify so aim for a marathon mid Feb, I usually aim around 30-40km a week start Jan and then add 5km per week from there trying to peak around 60-70km a week for a while.
Two oceans has its own decent training guides.
https://www.twooceansmarathon.org.za/ttom2024-training-guide/
