Perform the following steps to create your desired cluster with a determined size:

1. Using vSphere Web Client, log in to the vCenter Server.
2. Select the Hosts and Clusters view on the Home Screen.
3. Right-click on Datacenter in the Inventory tree and click on New Cluster.
4. Name this cluster in Cluster Creation Wizard.
5. Turn on vSphere HA and DRS.
6. Select all the default settings and click OK.
7. Once your cluster is created, right-click on it and select Add Host.
8. Specify the Hostname or IP Address of the ESXi hosts that you selected for your cluster and click Next.
9. Choose the default configuration for the rest of the steps and click on Finish.
10. Repeat steps 7 to 10 for the rest of the host's addition.

So, in a nutshell, if you limit the number of hosts in a vSphere HA cluster, then this reduces the number of load balancing opportunities. However, if you exceed the number of ESXi hosts beyond what you actually need, then this will cause CPU strain on your vCenter Server because DRS performs load balancing calculations every 5 minutes for each cluster. So this needs to be balanced according to your requirements.