Your USB boot drive is tiny. You cannot store VMs on the boot partition (best practice). For a portable lab:
To download the and prepare a portable installer, you must navigate the updated Broadcom support ecosystem. While "portable" usually refers to a bootable USB drive, the process starts with securing the correct image file. Step 1: Downloading the ESXi 7.0 ISO
Let us know in the comments if you need the direct MD5 checksum for the official ESXi 7.0 U3 ISO.
~600 words.
To make the installation process portable, you can use the portable version of to burn the ISO to a USB flash drive. Create a Bootable ESXi USB Flash Drive Installer - rufus
Once you've created the portable ESXi 7.0, you can boot from it by: