I would perform the steps in the exact order that I mentioned above. People with more knowledge than me will be able to answer this better, and if I’m mistaken someone please correct me, but per my knowledge, the opencore boot loader injects things into system memory instead of on disk.
“….OpenCore is a sophisticated boot loader used to inject and patch data in memory, instead of on disk…..”
So even if you wipe the drive, there still may be data left over that could interfere with a new native installation, so better to reset the NVRAM to clear that out after wiping the drive….. so I would go 123 like I mentioned above.
If downloading and installing Catalina from Internet recovery works for you, I guess you can do it that way, but a USB boot drive is a safe and sure thing to have on hand if you need to install macOS.