1) Run the vCenter appliance as one of the VMs on the vSphere environment. Now, you get 5 ESXi hosts and can make optimum use of them.
2) I assume you would have the physical RAID controller (as in the case of conventional HPE DL380 Gen10 servers). In that case, you would not need a third party utility to configure the RAID. You can create the required RAID from the RAID configuration utility.
With HPE servers, you have to access the Intelligent Provisioning tool during the startup (F10),
Then you select customize the RAID, using the smart array controller tool (By default, RAID 1 created for two disks),
Then you select that your OS is VMware ESXi, and then you attach the customized ISO for HPE : https://my.vmware.com/group/vmware/details?downloadGroup=OEM-ESXI67-HPE&productId=742
Noting that this RAID will be recognized by ESXi host as a data-store which provision many VMs.
And also as mentioned per my colleague SupreetK, no need to specify one ESXi hosts for vcenter VM. you can install vcenter on any host and group them for use for your workload.
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The BIOS in Gen10 has apparently changed since the previous posting. Currently in the Intelligent Provisioning Tool there is Perform Maintenance -option that has Intelligent Storage Configuration and RAID Configuration but I didn't find the option to set up OS on either of them.