I think you meant Forge instances instead of Homestead instances, right?
Using AWS auto scaling, or really anything in AWS to help automate new servers, won't be compatible with Forge in its current form as there's no API, giving you no way to not add a server info Forge without some manual work.
The easiest work around to this might be to use a load balancer in Forge and spin up 2+ servers in whichever cloud you use. Keep a server shutdown until you need it - if you can anticipate spikes, you can turn on a server when you need it, and add it to a load balancer when it has the latest version of your case base.
Keeping a load balancer around even when you only have one application server makes this fairly easy to do.