Do bidders have to set up a stripe account in order to bid?

Nope!

A Stripe account is required for the organization to receive the funds directly into its bank account. A bidder is required to have a credit card on file to bid. 

Stripe is completely hidden from bidders, and there's nothing extra for them to do! The only thing a bidder would see is a place to put in their credit card information when they are placing a bid or making a donation.