[CGamesPlay]

> If you do try to make the main volume seem "used", you run the risk of accidentally overwriting your hidden volume.

No, because during the normal use of the main volume, you provided the hidden volume password, so this was never a risk. So the the obvious answer to your question is therefore: use your main volume most of the time. Only switch to the hidden volume when you're doing your hidden activity.

FWIW, I also think that the whole scheme is better applied to external storage volumes rather than bootable OS volumes: a flash card with a main volume containing things a reasonable person would want to keep from accidentally being lost (tax documents, bank statements, and so on).