Multiple SSL certificates for ELB

You can have two certificates on two different ELB ports. You CAN'T have two certs on a single port. Most folks would want to use port 443 for SSL traffic so using another port may not be an option. You can use SAN or wildcard cert that can handle more than a single domain and assign that to a single port. 

Certificates are managed using IAM. More details here:http://docs.aws.amazon.com/IAM/latest/UserGuide/ManagingServerCerts.html

Memcache on AWS

ElastiCache is protocol-compliant with Memcached. Therefore, you can use standard Memcached operations likeget, set, incr and decr in exactly the same way as you would in your existing Memcached deployments.   Existing applications do not need to change and can simple 'pointed at' the ElastiCache service.  ElastiCache is exposed at the same port (11211) as default memcache port.  To configure and manage the cache servers for your application, you will need to use the AWS Management Console, CLI, SDK, or web services.