A:Answer In short: no, you don't have to use your existing keys. The lock comes with two keys and the deadbolt is pre-keyed for those keys.
For others who might be curious, though, you can use an included tool to pretty easily re-key the lock to work with your existing housekey (note: this works with existing kwikset keys; I had Schlage deadbolt/keys and the schlage key form factor did not fit into the kwikset key slot, so I could not rekey the kwikset to use with my existing house keys.