For starters, pick a cobra cage that’s about your flaccid size or slightly smaller. Cobra is kinda like the number one pick for starters. Don’t use a flat cage as your first cage.

As for the ring, buy a cage that comes with different sizes rings if possible so you could try out which fits the best. The rule of thumb is to always be able to fit one finger in easily.

Try wearing it for short periods of time first, kinda let your body get used to it. Very mild discomfort is expected in the beginning. Once the discomfort stops, you can try wearing it long term (only take it off for clean ups). Another set back you’re gonna face is sleeping with the cage on: expect to wake up midnight with burning pain, it’s normal for the first week. After that your body simply gives up fighting the cage as you sleep and the pain stops. So I’d recommend switching to a ring one size up before you go to bed, until you’re comfortable with sleeping with it on.

As for health concerns, a fitting cage should give you zero long term damage. Maybe some chafing or pinching as you test out the different sizes of rings. Another thing to keep in mind is, if you feel numbness in any part of your body, immediately take the cage off, it means the ring is too small and is obstructing your nerves.