While we do keep all necessary info regarding your order on hand, it is always a good idea to keep that for your personal records as well. Consider saving your Order Confirmation Email and the serial number for your bike(s). To find your serial number, check out this Help Center article.
Insuring your bike is another matter. Check with your personal insurance agent to see if they have options available for both covering your liability while riding the bike as well as ensuring that the bike is covered as personal property. While not all insurance companies have designed ebike specific policies, there are companies such as velosurance that specialize in bicycle specific insurance policies.