Though the speed improvements using HDFS are considerable, S3 did perform pretty well. At worst there's a 1.75x overhead in exchange for virtually unlimited scalability, 11 9's of durability and no worrying about over/under-provisioning storage space.
Names/Certificate is the limit on how many domain names you can include in a single certificate. This is currently limited to 100 names, or websites, per certificate issued.
Certificates/Domain limits how many certificates can be issued that contain a single registered domain*.
This is limited to 20 certificates per domain per week. Exception: When you request a certificate with the same exact set of FQDNs as previously-issued certificate, this rate limit does not apply, but the one below does.