You're only accepting donations, not payments for your service. You're basically working on tips that are given willingly, and guess what, you're rewarding them in-game for that. There's absolutely nothing wrong with that.
If you own money to PayPal, they'll try to reach you through 3rd parties to get their money back, Those 3rd parties are going to contact you and you can simply ignore them. There's almost nothing they can do to you. Imagine if PayPal would be suing every suspicions account that owns them money - that's a waste of money and resources right there.
If they'd care why those people are donating for your project, they'd ask more information from you, before allowing that to happen in the first place.
They can lock the accounts for up to 180 days because the default refund period is 180 days from the transaction date.