No EC2 from Amazon WebServices you can create the instance with 2 types of disks. Physical Disks ( EBS ) and Ephemeral Discs . Physical disks are the Magnetic Disk and SSD. The ephemeral disk is a memory disk and when the machine is turned off, data is lost. Some prefer to use ephemeral disk for swap and others for production. Some people put the site in GitHub and set up self-publishing on the site when it goes up, and in this case, the gain is exactly in the performance of a memory disk.
Yes, Auto Scaling allows this. You create a script in it that will load balancing between instances. Auto Scaling does not work directly with the instance. He works with the AMI image. To use you will need to create your AMI image and put the reference of it in the script. According to the balancing you set up it will either go up one instance or end with one, bringing the verticalization up or down.
Be very careful to create Spot Request instances. They are considered an auction. If the instance price exceeds the configured, your instance will be terminated without prompting. Reserved instances are cheaper, but you can not change the instance type after you've booked and it's a case for review.
What is your instance? What types of volume do you have? This information will help us to help you better.