I am coding with computercraft and I do not know where to post the questions - Arqade or Stack Overflow? Or both? If so how?
You should ask your ComputerCraft programming questions to StackOverflow with tag computercraft.
You can ask non-programming questions like (not sure what I can include, I didn't use ComputerCraft for years) crafting recipes of computers that come with ComputerCraft.
Please keep in mind that you are likely to get downvoted if you ask that question as it is a low effort question (can be found on mod's forum thread etc etc), however I hope that you get the base idea of "gameplay related parts to Arqade, code related parts to StackOverflow").