1. They will last for "several" years if stored properly - in a small, airtight, light-proof container; at steady room temperature (some people say to freeze them - I don't reccomend it). Time will take it's toll - but some seeds are still viable after more than 20 years.
2. Just like fine cigars - in humidores! Of course it must be properly dried and cured first, but there are pre-Castro, Cuban cigars, that have been kept in humidores for over 50 years - and have only gotten better in the process!