Is it all right to use alcohol to remove grease and oil from coins?
There may be additives in the alcohol which might react with the copper.
One comment, you mentioned rubbing the coins with cotton buds.This l would definitely advise against as this is what causes hairline scratches on proof and silver uncirculated coins.
The rule is never rub a coin with anything, as it could pick up grit and scratch the coin.
Always pat dry,or allow to air dry.
Numismatic is "King of Hobbies and Hobby of Kings".