Safety questions - open core install on MBP 2015 15"

Hi! I'd like to update my GF's mac according to this video:

https://www.youtube.com/watch?v=D8djeFJ1czU&ab_channel=AnsonAlexander

Only 16gb pendrive is enough for sure for the installation? I have retina MacBook Pro 2015 15" with OWC ssd (not the apple original one), is it working with that? How can I erase opencore or downgrade back to the last original OS (eg. Big Sur)? Thanks!!

submitted by /u/StunningReception584
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