Quick question, couldn't find any info when I skimmed the site

If I upload a game, and leave the voluntary donations up WITHOUT setting up any Paypal or Stripe on my account, what happens to any donations received? Do they just circle the void until a payment system is set up, do they get refunded, or does itch just take it? 

If you let Itch.io collect payments for you, then the money accumulates in your account. You'll have to claim it after a while or lose it, but you don't have to connect your PayPal account right away.