You can only pick one person to display as your busker, but you can have an unlimited number of People cards (unlimited for each person) -- and those cards stack to give you a grand total of fans, skill, luck, and IM (income modifier).
A couple useful websites can help you find good value on cards and purchase them from the market:
FoxOn's website: https://rsgfam.com/shop/fans
NFTMart: https://nftm.art/buy/star