I am looking to install the free version of ESXI on my server but am possibly upgrading it in the future. I currently have 1 CPU and 48GB of RAM. I would be looking to add another CPU and memory for it. Would ESXI be able to handle the upgrade or would I have to reinstall it so it could see the 2nd CPU?
VMware will recognize your new hardware upon reboot.
You won't need to make any changes to the ESXi configuration for the hardware changes you've described.