EKS Auto-mode, how to set limits on the nodes

I'm trying to figure out how I can limit the automatically generated nodes to a max of 5 instances and only medium instances for example.

I tried creating my own node pool as per the docks here: https://docs.aws.amazon.com/eks/latest/userguide/create-node-pool.html

but i get an error stating the 'node_pools' can only be 'system' or 'general-purpose'

So how do i assign my node pool to the auto-mode cluster?

I'm just starting with EKS auto-mode and scratching my head, in addition to how to set limits. i'm curious why, when i launched the 2048 Game example it create two "xl" instances anyway. is that really the best option for a small application like that?

Thank you