Generally a good idea!
However regard, that OnlyFans has its office in GB (former EU member) and, I guess, hasn't abolished all of the legal stuff the EU has raised over the years.
This includes all the "prevention of money laundering acts", meaning, that all of the so called "prepaid CCs" have to be personalised with the issuing bank.
So lucky USA, if you still can buy these cards without any identification.
The other question then will be, whether OF will accept your prepaid card. Perhaps you should check before buying such a card.
Good luck!