I incorporate chastity into sessions frequently. you can read more about that in a topic titled "Chastity" on My Domme Board. http://coot.arvixe.com/~domroot/thebuzz/ubbthreads.php?ubb=showthreaded&Number=121#Post121

To specifically answer your questions:

Typically I only put a sub in chastity for a week or less. Wearing a device any longer than that without removing if for cleaning can cause problems.

Most issues with chastity have to do with the device rubbing, pinching or otherwise causing irritation due to an ill fitting device. The stock devices are uncomfortable for most wearers. Oddly enough the metal devices tend to be more comfortable (and hygienic for longer term wear) and wearers get used to the weight relatively quickly.

I normally use the plastic numbered locks so the sub can cut himself out in the event of an emergency. He had better arrive with that lock in place or he is in trouble. If I am going to allow him to let himself out, he has to send Me photographic proof that the lock is in place before he is allowed to cut. I always set a penalty for removing the device early. This is negotiated up front. This can be anything from a monetary fine to a certain number of cane strokes.

In My experience long chastity agreements work best in lifestyle situations where the Mistress can oversee the removal daily for cleaning. I work with two couples where the wife keeps the husband in long term chastity - so it can be done - but it is usually not feasible for a professional Mistress to keep a sub locked away for longer than a couple of weeks. I know of exceptions but it's very labor intensive for the Domme. I also see a sub that serves an online chastity Mistress. (She sends him to Me from time to time.) Again, they communicate via cam almost daily. In all three of these situations, the men wear custom made devices.

The idea of sending a sub off in a CB6000 for a 3 months is more a fantasy than a reality.