All Idealstack plans support unlimited sites. By using enough stacks and large enough instances and enough of them you can host as many as you want, including a mix of large and small sites.  

There are some fundamental limitations on the AWS load balancer that limits how many sites can be run per stack:

• A maximum of 25 SSL certificates per load balancer.  This limits you to 25 sites with SSL certificates.
  • One way around this however is to use Cloudfront in front of Idealstack and host the SSL certificates on that instead of Idealstack
• A max of 100 'rules' for the ALB.  If you use SSL for a site each domain will consume 2 rules, if you don't it will consume 1.  This means a max of 100 domains per stack (100 sites if they each have one domain, but less if they have more)

 

As a general guide - we find that on a t2.micro instance (ie the AWS free tier) you'll get about 3 moderate traffic sites.  Using two t2.medium instances with autoscale (our 'recomended' stack, see above) you can reach the ALB limits for low traffic sites.  By adding more instances (automatically using autoscale or manually) you can handle higher traffic sites

The Professional plan  supports having more than one stack, possibly in different regions