vRealize Automation you can deploy in three size Small, Medium or Large. The Small deployment
Medium
Large
Based on that configuration recommended by vMware you can choose your solutions based for your recomendation. Of course you can go with small and after some time when you require more and more you can add other element to your infra.
To add other elements to infrastructure you need to configure load balancer based on vMware guide
For version 7.4
https://docs.vmware.com/en/vRealize-Automation/7.4/vrealize-automation-load-balancing.pdf
For version 7.5
https://docs.vmware.com/en/vRealize-Automation/7.5/vrealize-automation-load-balancing.pdf
and add other services to infrastructure using the IaaS Installer
